I'd speak with the dive op of your choice and ask them. While Keys tourism is insane during the winter months, the summer is the busier diving season due to the water being warmer, and usually calmer. You can call a few dive ops and interview them over the phone to get a feel for things. Ask to speak to the owner or manager. I still highly recommend Conch Republic. When you call them, ask for Brenda or Gary and if they are not around, ask for Capt. Dan.
However, I would book my lodging for Dec/Jan yesterday. However, the dive op of your choice may have lodging specials with whatever motel they work with, so maybe start there.
BTW your non-diving family will LOVE the Key Largo Princess glass bottom boat, and Theater of the Sea, and Robbies' Marina (feeding the tarpon). Stop at the A-Frame Visitor Welcome center at MM106.3 on the left just as you enter the Keys, they have coupons for those and a free attractions map. (I used to work there and it is well worth it to stop in for freebies and advice.)
