If one member of a family is a Federation member, and the remainder of the household becomes members, how is the household charged?

Household memberships are activated from the day the payment is received unless they are reactivating an existing expired membership.

All members activating are given 12 months of membership into the future  (or from the existing membership expiration date) plus the person who already had membership.

For example, when 2 members activate a Household membership and 1 other person already had an individual membership, if the existing member has 6 months remaining, then those six months are allocated across all 3 memberships to extend their expiration date.

Each Household member's membership would be extended an additional 2 months, so at the time the household is activated all three would get 15 month memberships, so they do not lose any paid time.