Since the original poster lists a fairly low dive count and per profile has been certified under a year, I suppose he may not have done much foreign travel to the Caribbean region (speculation on my part; he may be a seasoned traveler), so some added comments.
At least via live-aboard, diving out of Provo. is known for being rather deep (the top of the reef wall starting maybe 45 - 50 feet or so?). If you're fairly fresh out of open water training, you might want a destination tending toward somewhat shallower diving. Also, it is 'wall' diving - most of what we did started over a flat sandy plain, but we swam out to the wall and then is was swimming along a variably vertical wall, with the bottom way below. I just want it clear that a lot of scuba diving doesn't involved swimming over a flat 'floor' 10 to 20 feet under you.
While we've spoken of diving and trip costs, since this is a family vacation, be mindful the topside experience (outside the beach) varies a lot. The lushly vegetated St. Lucia was beautiful, St. Croix more 'gently mountainous' over part of it, Curacao is arid with some cacti, etc... But that's not what I'm getting at...
Some islands are particularly 'touristy.' While some don't like that, people looking for topside excursions to entertain kids & other family members may have a different perspective. Islands taking a lot of cruise ships often offer a lot of excursions. Grand Cayman is a popular cruise port (thus the capital can get congested hours they're in port); it's got a Turtle Farm (sea turtle production) and dolphin encounter option (disclaimer: many people are opposed to captive marine mammal 'exploitation' and some don't like the turtle farm; make up your own mind). Cozumel has various options (including dolphins). Provo. is not a cruise port...but Grand Turk is.
You can go to TripAdvisor.com, put in your destination and go to their 'Things To Do' category, and that'll give you topside options. If one family member is bent on trying zip lining, would carry the treasured memory of an in water hands-on dolphin encounter till death, etc..., that might narrow it down. And if you like your topside a little less touristy, St. Croix might be just right.
Richard.