Wow, that sounds like fun!!
With respect to Balimaiz, even if you ARE travelling with your family, you will absolutely enjoy bringing your gear and enjoying some riding on each of these beautiful islands!
Certainly St. Lucia should have fantastic wind in April! If you're on a ship, you probably will be on the north end of the island - there you will find Tornado Center. Please contact them for riding details and info-
If you want to head to the south part of the island, Vieux Fort, then The Reef is where you'll want to be!
Barbados has amazing riding and some of the best waves in the Caribbean - SkyRiders (Club Mistral) has an operation there - check out their website for details -
For St. Maarten, I think you can find good details on the site http://www.tropical-paradise.net
I can get you details pretty soon for Grenada - the Best Offhsore Odyssey is just returning from their maiden voyage, and Grenada was their starting point! Let me know if you would like the info...
Tortola I don't know at all, but I"m quite sure someone out there does!
Hope this helps. Let me know if I can be of further assistance!