I always wonder why people consider doing a scuba class while on vacation to be "wasting valuable time."
There is no reason that learning to dive should not be as much fun as "diving" itself is. Most instructors don't get this... and a lot of students/divers don't either.
All of you doing the class will keep you all together, which is obviously and important part of a family vacation.
I suggest you call the shop back and re-frame your question: "We want to have fun on our vacation - including during the certification process - can you guarantee that we'll have fun doing the confined water sessions with you?"
If they hesitate for even a moment, find another shop/instructor.
If you can't find a shop that will guarantee that you'll have fun learning to dive with them... shoot me a PM. I'll fly down to the Keys and do an OW class for your kids, and you and the wife can join us as a refresher for free. (If you and wife want to get a brand new OW c-card in the process it's easy enough, and cheap, to process the paperwork for two more certs.)