Welcome aboard, Mindy! Your boys are at such a great age to experience the magic of setting sail on the Disney Fantasy.
I think your whole family will love your chosen Port Adventure in Tortola. Getting a 40-minute tour of that gorgeous island (complete with photo stops, which you'll want to take full advantage of!), and then having hours to relax and play on the
beaches at Baths is a great way to spend the day. The boys will especially love the caves on the beach that they can explore.
Since you'll be spending beach time on Tortola and Castaway Cay, I'd recommend something different in Tortola. The island is famous for Coral World and the Butterfly Garden, both of which are offered as individual or combo Port Adventures. My kids think it's pretty cool to walk into a little paradise of butterflies, and I think your boys would really enjoy this. Your driver guides will point out sights as you drive to and from, almost like a mini-island tour on your way to your main adventures. Plus, you'll get some spectacular views.
But, speaking of views, a quick and easy adventure is to take the
Skyride to Paradise Point. Talk about a view from the top of the world! Since guests do this adventure on their own time, you can take a Port Adventure first thing in the morning, then walk across the street from the port when you return and head up to Paradise Point on this tram in the air. The ride alone is an adventure for my kids! Do a little shopping and sight-seeing then head back down to the ship. The price is the same if you pre-book this through Disney or buy tickets at the last minute at the gate, so if you find that day you'd like to go, it's easy to do!
Have fun planning your adventures, Mindy!
Marcy