Houston Museum / Culture gift memberships?

Hi – I'm wondering if there's any type of 'mega membership' for Houston's Museum Campus? I'm trying to find a gift for my brother and his partner that would allow them to visit as many places as possible, not just one place – if that makes sense.

I'm imagining something like those paper coupon books you used to be able to buy, but for museums and cultural events. Any ideas? They already have a membership to the Natural Science Museum, and worst case scenario I'd just get them another membership.

Thanks for any leads or ideas!