What does it cost for family membership

They don't offer family memberships. The cost is approximately $15 for residents and $18 for non-residents. Children under 4 are free. With a membership, you also get access to most fitness classes and the swimming pool.

So

I do the day pass for $6 a visit.

There's no family membership. If you have a membership, the rest of your family can join without paying the first time membership fee.