How to tell different types of Logins apart and how to see the users?
Yes the icon changes if it's a group vs a user. You can also query sys.server_principals.

To see the users within an AD group, you can use xp_logininfo. As long as the AD group is a login on the SQL Server, you can query it using xp_logininfo. Here's a really old blog post I wrote on it.

Syntax:

xp_logininfo [ [ @acctname = ] 'account_name' ] 
     [ , [ @option = ] 'all' | 'members' ] 
     [ , [ @privilege = ] variable_name OUTPUT]


Example:

EXEC master.dbo.xp_logininfo 'DomainName\GroupName', 'members'