Do You Have To Be A Good Swimmer To Snorkel Which Of These Islands Is Best For Snorkeling Or An Off-road Jeep Tour?

Which of these islands is best for snorkeling or an off-road jeep tour? - do you have to be a good swimmer to snorkel

My friend and I are going on a cruise in the Caribbean in late October / early November and I want to know what activities (do any of us to have ever been) in the Caribbean.

Here is the itinerary:
Leaving San Juan, Puerto Rico
St. Croix, U.S. Virgin Islands
St. Kitts
Dominica
Saint Lucia
Barbados
Grenada
Day at the beach
Curacao
Aruba
Day at the beach
Back in San Juan

This island offers the best snorkeling? By "better" I mean a lot to see and for two people who are not great swimmers, and not much snorkeled. (I've heard Buck Iceland, near St. Croix is good, but the water can be hard.) If possible, I prefer it in the first half of the SnorkelTrip.

What would you suggest to take a tour of the island in front of the jeep in the street? I think Dominique, because it seems that most of nature, but I'm not sure.

In addition, all "can not lose" points of interest or expertise in one of the islands? Thank you!