If you are doing the itinerary with St. Johns, Antigua, I recommend www.adventureantigua.com
with Eli and his eco tour. You get on a catamaran, get a wonderful tour by water of Antigua, swim, snorkel and go to I think its called Bird Island, which is amazing with a beach and a small hike to the top of little mountain...easy to do with kids for a real treat of native birds. Don't miss this one.
another catamaran snorkel tour with a very small group...just terrific.
Have a blast.