This screen really defines Contacts and their Memberships.

A contact is a member, an entrant, a stallholder or just someone (or something) that you wish to keep personal details on.
A contact does not have to have any Memberships defined for it.

Family Memberships:
One method is to specify two different categories. The main contact person of the family has a Category of "Family Membership - Contact" that has the fee associated with it and other members of the family all have the Category "Family Membership". Alter the Member# manually so that all have the same number.

Show Membership Screen:

List Personal Information:

List Membership Information: