Southern Carribean Cruise Dive Recommendations

[waoop]

Going on a cruise of the Southern Caribbean in April and looking for recommendations. We'll be with teenage daughters who like to snorkel but are not divers. We can probably get away with two (maybe three) dive days during the week, so I'd like to pick the best spots on the trip. Here's the itinerary:

St. Thomas
Dominica
Barbados
St. Lucia
St Kitts
St. Maarten

Thanks!