My family and I are also going on the Conquest on June 7th! We really haven't picked any of our excursions, though we are definitely booking through Carnival for any Montego Bay excursions. For Grand Cayman, we're willing to do non-Carnival excursions. I'm really leaning toward the dolphin swim at Montego Bay, but we'll probably just decide as we go..we don't like to plan much when we're on vacation. The only thing we are "for sure" doing is eating at "The Reef Grill" in Grand Cayman, we have family friends who rave about it every time they travel to GC.
For the excursions, when I glance through them my only advice would be that some of them have long rides, specifically the kid-oriented ones (such as the Waterpark with a 75 minute drive to get there). I don't know how your kids are with riding, but I would say that wouldn't be something I would want to do with children, personally, lol.
My parents are in their late 40s, and my brother and I are both 18, recently graduated. To get an idea of more ages of people going on the cruise, here's another thread to glance through:
http://boards.cruisecritic.com/showthread.php?t=904473. Seems like there will be a lot of kids!