Question

how do I become a Family Member versus a guest member

Answer 1

This info comes from the help index under Wikitree:

 

You get a Family Member account in one of two ways:

1. A current member adds you as a family member or friend. They include an e-mail address on your profile and you accept the invitation.^[1]
2. You register as a Guest Member and a Wiki Genealogist confirms you. Unless you volunteer to do wiki genealogy yourself they would only do this if they intend to help with your genealogy.