Difference between 成员 and 会员?
成员 means member in a generic sense. 

It can refer to a member of any organization, like a team (e.g. 团队成员), a class (e.g. 班级成员), a party (e.g. 党派成员), a tribe (e.g. 部落成员), a crew (e.g. 机组成员), a committee (e.g. 委员会成员), the jury (e.g. 陪审团成员), etc. 

It can be extended to mean an element/component/constituent of an object, for example in Computer Programming, a variable defined on a class is called 成员变量.



会员 also means member but with much narrower usage. It is used only when 


The organization is a membership club, e.g. 俱乐部会员 -or-
The Chinese translation of the organization ends with 会, e.g. 国会会员. 


Generally, 会员 can be replaced with 成员 but not the other way round. 俱乐部成员 sounds equally correct and natural as 俱乐部会员, but for member of the jury you can only say 陪审团成员 while 陪审团会员 is wrong and sounds funny.