How do I determine if membership in a DB fixed role is by direct user memership or through membership in a custom DB role?
I'm not sure of the answer about the sp_helprolemember, but when I'm looking into user permissions, I use the query below.  It's very much a work in progress and I'm always tweaking something about it.  Designed for SQL2012.  

/****************
Name: User Analysis Mk2
Author: Jonathan Fite
Date: 1/23/2015

Purpose: To display the individually set permissions for every user in the current database. 

USAGE: Execute script to see details of what type of access has been granted where.

NOTES:
    - Recursive, so that a user who is a member of a role, which is a member of a role is displayed, use
        the "RoleGrantedThrough" column to see this recursiong.
    - But selecting to a specific value in the "UserName" column, will show you everything that user has. 
    - Displays relevant objects that has been granted to.  

FIX QUERIES:
    There are a few fix queries at the bottom of this file (commented out) that are designed to help with 
    targeting and resolving specific issues.  Orphaned Users, Schema Ownership, etc.  

    Usage for these is recommended to target a specific issue such as orphaned users, fix that issue to your
    satisfaction and then run this script again before targeting a second "issue".  

    Targeted Issue Fix:
        - Orphaned Users - Identify users who don't have a link to a server level account, then script out
            their removal.  Handles whether they own schemas or not.

        - Fix Schemas owned by Orphaned Users - Identify schemas that are owned by orphaned users (without fixing
            the orphaned user issue).  Schemas with no objects are dropped.  Schemas with objects have their
            ownership changed to dbo.  

        - Fix GRANT_WITH_GRANT_OPTION - Identify permissions where a user is able to further grant permissions to others.
            Their permission will be changed to just "GRANT".

        - Fix REFERENCE - Identify REFERENCE permissions and remove the permission completely.  



OUTPUT:

    #UserPermissions
    - ServerName - the name of the server.
    - DatabaseName - the name of the database (For server level, the database is null).
    - UserName - the name of the user.
    - SID - the SID of the user in question (for tracking up to sys.server_principals if desired).
    - RoleName - the name of the role.
    - Usertype - the type of user (U,G,R, etc.)
    - UserTypeDescription - the description of the user type.
    - DefaultSchema - the users default schema.
    - create_date - the date the user was created.
    - GrantedThroughName - the name of the role that the access was granted through.
    - SchemaName - the schema of the object in question.  NULL or blank typically means it's a database level permission.
    - ObjectName - the name of the object in question.  NULL or blank typically means it's a database level permission.
    - ObjectType - the type of the object in question.
    - PermissionScope - the scope of the permission (DATABASE, OBJECT_OR_COLUMN, etc.)
    - Permission_Type - the type of the permission.
    - Permission_TypeName - the type of the permission (in english).
    - Permission_State - the state of the permission (GRANT, DENY, etc.)

    #OwnedSchemas
    - ServerName - the name of the server.
    - DatabaseName - the name of the database.
    - SchemaName - the name of the schema.
    - OwnerName - the name of the owner.
    - OwnerSID - the owner's SID
    - OwnerType - the owner user type.
    - OwnerTypeDesc - the owner's type description.
    - ObjectCount - the number of objects that belong to the schema. 

More Information: https://msdn.microsoft.com/en-us/library/ms191291.aspx

********************/

--Table to hold User Permissions
IF(OBJECT_ID('tempdb..#UserPermissions') IS NOT NULL)
BEGIN
    DROP TABLE #UserPermissions 
END

CREATE TABLE #UserPermissions
    (
    ServerName SYSNAME NULL
    , DatabaseName SYSNAME NULL
    , [SID] VARBINARY(85) NULL
    , ServerUserName SYSNAME NULL
    , DatabaseUserName SYSNAME NULL
    , RoleName SYSNAME NULL
    , RoleOwnerName SYSNAME NULL
    , UserType CHAR(1) NULL
    , UserTypeDesc VARCHAR(50) NULL
    , DefaultSchema SYSNAME NULL
    , DateCreated DATETIME2 NULL
    , RoleGrantedThrough SYSNAME NULL
    , SchemaName SYSNAME NULL
    , ObjectName SYSNAME NULL
    , ObjectType VARCHAR(200) NULL
    , PermissionScope VARCHAR(200) NULL
    , PermissionType VARCHAR(10) NULL
    , PermissionTypeName VARCHAR(200) NULL
    , PermissionState VARCHAR(100) NULL
    )

--Table to hold Schema Information...
IF(OBJECT_ID('tempdb..#OwnedSchemas') IS NOT NULL)
BEGIN
    DROP TABLE #OwnedSchemas 
END

CREATE TABLE #OwnedSchemas
    (
    ServerName SYSNAME NULL
    , DatabaseName SYSNAME NULL
    , SchemaName SYSNAME NULL
    , OwnerName SYSNAME NULL
    , OwnerSID VARBINARY(85) NULL
    , OwnerType CHAR(1) NULL
    , OwnerTypeDesc VARCHAR(50) NULL
    , ObjectCount INT NULL
    )

--Server Level Permissions...
;WITH ServerRoles (member_principal_id, role_principal_id, GrantedThrough)
AS
(
SELECT rm1.member_principal_id
    , rm1.role_principal_id
    , NULL AS GrantedThrough
FROM sys.server_role_members rm1 (NOLOCK)
UNION ALL
SELECT P.principal_id
    , NULL
    , NULL
FROM sys.server_principals P (NOLOCK)
UNION ALL
SELECT d.member_principal_id
    , rm.role_principal_id
    , d.role_principal_id AS GrantedThrough
FROM sys.server_role_members rm (NOLOCK)
    INNER JOIN ServerRoles d ON d.role_principal_id = rm.member_principal_id 
)
--Use distinct to get rid of things like public repeating for each user...
INSERT INTO #UserPermissions
SELECT DISTINCT @@SERVERNAME AS ServerName
    , NULL AS DatabaseName
    , UseRolePrincipalrincipal.[sid]
    , UseRolePrincipalrincipal.name AS ServerUserName
    , NULL AS DatabaseUserName
    , RolePrincipal.name AS RoleName
    , RoleOwner.name AS RoleOwnerName
    , UseRolePrincipalrincipal.[type] AS UserType
    , UseRolePrincipalrincipal.type_desc AS UserTypeDesc
    , NULL AS DefaultSchema
    , UseRolePrincipalrincipal.create_date
    , GrantedViaPrincipal.name AS RoleGrantedThrough
    , NULL AS SchemaName
    , NULL AS ObjectName
    , NULL AS ObjectType
    , DBPerm.class_desc AS Permission_Scope
    , DBPerm.[type] AS Permission_Type
    , DBPerm.[permission_name] AS Permission_TypeName
    , DBPerm.state_desc AS Permission_State
FROM ServerRoles drm
    LEFT OUTER JOIN sys.server_principals RolePrincipal ON RolePrincipal.principal_id = drm.role_principal_id
    LEFT OUTER JOIN sys.server_principals UseRolePrincipalrincipal ON UseRolePrincipalrincipal.principal_id = drm.member_principal_id
    LEFT OUTER JOIN sys.server_principals RoleOwner ON RoleOwner.principal_id = RolePrincipal.owning_principal_id
    LEFT OUTER JOIN sys.server_principals GrantedViaPrincipal on GrantedViaPrincipal.principal_id = drm.GrantedThrough 
    LEFT OUTER JOIN sys.server_permissions DBPerm ON DBPerm.grantee_principal_id = CASE WHEN drm.role_principal_id IS NULL THEN drm.member_principal_id ELSE drm.role_principal_id END

DECLARE @DatabaseName SYSNAME
DECLARE @Query NVARCHAR(4000)

DECLARE curDB CURSOR LOCAL STATIC FORWARD_ONLY
FOR SELECT D.name
    FROM sys.sysdatabases D
    ORDER BY D.name 

OPEN curDB

FETCH NEXT FROM curDB
INTO @DatabaseName

WHILE @@FETCH_STATUS = 0
BEGIN

    --Get the User Permission Information.
    SET @Query = 'USE ' + QUOTENAME(@DatabaseName)
        + ' ;WITH RoleMembers (member_principal_id, role_principal_id, GrantedThrough )
            AS
            (
            SELECT rm1.member_principal_id
                , rm1.role_principal_id
                , NULL AS GrantedThrough 
            FROM sys.database_role_members rm1 (NOLOCK)
            UNION ALL
            SELECT P.principal_id
                , NULL
                , NULL AS GrantedThrough
            FROM sys.database_principals P
            UNION ALL
            SELECT d.member_principal_id
                , rm.role_principal_id
                , d.role_principal_id AS GrantedThrough
            FROM sys.database_role_members rm (NOLOCK)
                INNER JOIN RoleMembers d ON d.role_principal_id = rm.member_principal_id
            ) 
            --Use distinct to get rid of things like public repeating for each user...
            INSERT INTO #UserPermissions
            SELECT DISTINCT @@SERVERNAME AS ServerName
                , DB_NAME() AS DatabaseName
                , UserPrincipal.[sid]
                , ServerPrincipal.name AS ServerUserName
                , UserPrincipal.name AS DatabaseUserName
                , RolePrincipal.name AS RoleName
                , RoleOwner.name AS RoleOwnerName
                , UserPrincipal.[type] AS UserType
                , UserPrincipal.type_desc AS UserTypeDesc
                , UserPrincipal.default_schema_name AS DefaultSchema
                , UserPrincipal.create_date
                , GrantedViaPrincipal.name AS RoleGrantedThrough
                , S.name AS SchemaName
                , O.name AS ObjectName
                , O.type_desc AS ObjectType
                , DBPerm.class_desc AS Permission_Scope
                , DBPerm.[type] AS Permission_Type
                , DBPerm.[permission_name] AS Permission_TypeName
                , DBPerm.state_desc AS Permission_State
            FROM RoleMembers drm
                LEFT OUTER JOIN sys.database_principals RolePrincipal ON RolePrincipal.principal_id = drm.role_principal_id
                LEFT OUTER JOIN sys.database_principals UserPrincipal ON UserPrincipal.principal_id = drm.member_principal_id
                LEFT OUTER JOIN sys.database_principals GrantedViaPrincipal on GrantedViaPrincipal.principal_id = drm.GrantedThrough 
                LEFT OUTER JOIN sys.database_principals RoleOwner ON RoleOwner.principal_id = RolePrincipal.owning_principal_id
                LEFT OUTER JOIN sys.database_permissions DBPerm ON DBPerm.grantee_principal_id = CASE WHEN drm.role_principal_id IS NULL THEN drm.member_principal_id ELSE drm.role_principal_id END
                LEFT OUTER JOIN sys.objects O ON O.[object_id] = DBPerm.major_id AND DBPerm.class = 1
                LEFT OUTER JOIN sys.schemas S ON (S.[schema_id] = O.[schema_id] AND DBPerm.class = 1) OR (DBPerm.class = 3 AND S.[schema_id] = DBPerm.major_id)
                LEFT OUTER JOIN sys.server_principals ServerPrincipal ON ServerPrincipal.[SID] = UserPrincipal.[SID]'

        EXEC sp_executesql @Query 

        --Get the Schema Information...
        SET @Query = 'USE ' + QUOTENAME(@DatabaseName)
            + ' INSERT INTO #OwnedSchemas
                SELECT @@SERVERNAME AS ServerName
                , DB_NAME() AS DatabaseName
                , S.name AS SchemaName
                , P.name AS OwnerName
                , P.[SID]
                , P.[type] AS OwnerType
                , P.type_desc AS OwnerTypeDesc
                , COUNT(O.object_id) AS ObjectCount
            FROM sys.schemas S
                LEFT OUTER JOIN sys.objects O ON O.schema_id = S.schema_id
                LEFT OUTER JOIN sys.database_principals P ON P.principal_id = S.principal_id
            GROUP BY S.name
                , P.name 
                , P.[SID]
                , P.[type]
                , P.type_desc'

        EXEC sp_executesql @Query 

        --Loop to the next database.
        FETCH NEXT FROM curDB
        INTO @DatabaseName

END

CLOSE curDB
DEALLOCATE curDB

SELECT * FROM #UserPermissions

SELECT * FROM #OwnedSchemas

/*** Some Useful Queries


--Distinct Permission Types.
SELECT DISTINCT PermissionType, PermissionTypeName
FROM #UserPermissions
ORDER BY PermissionType


--High Privilege Accounts...
--ALTER objects, Impersonate, Control, Create Tables, Reference Objects, Take Ownership or can GRANT to others.
--or members of db_owner, ddladmin , securityadmin, sysadmin on either database or server levels. 
SELECT * 
FROM #UserPermissions
WHERE PermissionType IN ('IM', 'AL', 'CL', 'CRTB', 'RF', 'TO')
    OR PermissionState = 'GRANT_WITH_GRANT_OPTION'
    OR RoleName IN ('db_owner', 'db_ddladmin', 'db_securityadmin', 'sysadmin', 'securityadmin', 'serveradmin')

**/


/*** Generate Fix Scripts.

    The fix scripts below will generate various fix scripts for certain conditions.  
        I.E. - fix users who can grant permissions.


******************************************************************************************************************
//////////////////////////////////////////////////////////////////////////////////////////////////////////////////
******************************************************************************************************************

--Fix Schemas owned by orphaned users.
--If the schema has objects, change the owner to dbo.  
--If the schema does not have objects, drop the schema.
;WITH OwnedSchemaFix
AS
(
SELECT OS.*
    , P.name AS ServerUserName
FROM #OwnedSchemas OS
    LEFT OUTER JOIN sys.server_principals P ON P.[sid] = OS.OwnerSID
WHERE OwnerType = 'U'
    AND P.name IS NULL      
)
SELECT ServerName   
    , DatabaseName
    , SchemaName
    , OwnerName
    , OwnerType
    , FixStatement = CASE   WHEN ObjectCount = 0
                                THEN 'USE ' + QUOTENAME(DatabaseName) + '; DROP SCHEMA ' + QUOTENAME(SchemaName)
                            WHEN ObjectCount &lt;&gt; 0
                                THEN 'USE ' + QUOTENAME(DatabaseName) + '; ALTER AUTHORIZATION ON SCHEMA:: ' + QUOTENAME(SchemaName) + ' TO [dbo]'
                            END
FROM OwnedSchemaFix 

******************************************************************************************************************
//////////////////////////////////////////////////////////////////////////////////////////////////////////////////
******************************************************************************************************************

--Fix Orphaned Users
--Change owner of schema or drop schema (if no objects).
--Drop the user.
;WITH OrphanedUserFix
AS
(
SELECT DISTINCT U.ServerName
                , U.DatabaseName
                , U.DatabaseUserName
                , U.ServerUserName
                , U.[SID] 
FROM #UserPermissions U
WHERE U.DatabaseName IS NOT NULL --Only want database level accounts.
    AND U.ServerUserName IS NULL --No entry in sys.server_principals.
    AND U.UserType &lt;&gt; 'R' --Ignore roles.
    AND [SID] &lt;&gt; 0x00 --Ignore system generated users.
)
SELECT E.*
FROM    (
        --Drop Schemas First.
        SELECT F.ServerName
            , F.DatabaseName
            , F.DatabaseUserName
            , F.ServerUserName
            , FixStatement = CASE WHEN S.ObjectCount &lt;&gt; 0 THEN 'USE ' + QUOTENAME(F.DatabaseName) + '; ALTER AUTHORIZATION ON SCHEMA:: ' + QUOTENAME(S.SchemaName) + ' TO [dbo];'
                                    ELSE 'USE ' + QUOTENAME(DatabaseName) + '; DROP SCHEMA ' + QUOTENAME(SchemaName)
            , FixStatementInt = 1
        FROM OrphanedUserFix F
            INNER JOIN #OwnedSchemas S ON S.OwnerSID = F.[SID]
        UNION ALL
        --Drop Users Second.
        SELECT F.ServerName
            , F.DatabaseName
            , F.DatabaseUserName
            , F.ServerUserName
            , FixStatement = 'USE ' + QUOTENAME(F.DatabaseName) + '; DROP USER ' + QUOTENAME(F.DatabaseUserName)
            , FixStatementInt = 2
        FROM OrphanedUserFix F 
        ) E
ORDER BY E.DatabaseName, E.DatabaseUserName, E.FixStatementInt, E.FixStatement

******************************************************************************************************************
//////////////////////////////////////////////////////////////////////////////////////////////////////////////////
******************************************************************************************************************

--Generate script to fix GRANT_WITH_GRANT_OPTION
--This will revoke all rights for principals to subsequently pass their permissions onto others.  

;WITH GrantFix
AS
(
SELECT *
FROM #UserPermissions
WHERE PermissionState = 'GRANT_WITH_GRANT_OPTION'
    AND RoleName IS NULL
)
SELECT DatabaseName 
    , ServerUserName
    , DatabaseUserName
    , SchemaName
    , ObjectName
    , PermissionType 
    , PermissionTypeName
    , PermissionState 
    , FixStatements = 'USE ' + QUOTENAME(DatabaseName) + '; REVOKE GRANT OPTION FOR ' + PermissionTypeName + ' ON ' + QUOTENAME(SchemaName) + CASE WHEN ObjectName IS NULL THEN '' ELSE ('.' + QUOTENAME(ObjectName)) END + ' TO ' + QUOTENAME(DatabaseUserName) + ' CASCADE AS [dbo];'
FROM GrantFix
WHERE DatabaseName IS NOT NULL  
ORDER BY DatabaseName, ServerUserName, DatabaseUserName, SchemaName, ObjectName, PermissionTypeName

******************************************************************************************************************
//////////////////////////////////////////////////////////////////////////////////////////////////////////////////
******************************************************************************************************************

--Generate script to remove all permissions to use REFERENCE.
--REFERENCE allows users to create objects that have FK references to other tables.
;WITH ReferenceFix
AS
(
SELECT *
FROM #UserPermissions
WHERE PermissionType = 'RF'
    AND PermissionState = 'GRANT'
    AND RoleName IS NULL
)
SELECT DatabaseName 
    , ServerUserName
    , DatabaseUserName
    , SchemaName
    , ObjectName
    , PermissionType 
    , PermissionState 
    , FixStatements = 'USE ' + QUOTENAME(DatabaseName) + '; REVOKE ' + PermissionTypeName + ' ON ' + QUOTENAME(SchemaName) + CASE WHEN ObjectName IS NULL THEN '' ELSE ('.' + QUOTENAME(ObjectName)) END + ' TO ' + QUOTENAME(DatabaseUserName) + ' CASCADE AS [dbo];'
FROM ReferenceFix
WHERE DatabaseName IS NOT NULL



******************************************************************************************************************
//////////////////////////////////////////////////////////////////////////////////////////////////////////////////
******************************************************************************************************************


****/