Must be in a type of group to join other groups (ie. group joins groups)

We have a client that wants to group users as families and only allow the families to join groups.

We are pretty new to BuddyPress and aren’t quite sure the best way to approach this. If there is no easy/cheap way to do this, we may just go with one user login = the family, but the client isn’t super excited about that solution.

Is there a pre-made solution or something I’m missing because of my unfamiliarity with BP?