We just returned from a great Disney Magic Eastern Caribbean cruise. I think your family will enjoy the ship -- there's almost too much to do! They seem to have a good teen program in addition to a very popular youth program.
Actually what we spent a lot of money on is the many professional photographs of our family -- either in formal portraits or with the characters. Also, be prepared to spend money at the game arcade since your kids seem to be prime age for that.
I had a wonderful massage at a cabana on Castaway Cay, Disney's private island. Talk about relaxation! These go quickly so make your way to the spa upon embarkation. As on most cruise ships, a basic massage is expensive -- $115.
As for shore excursions, you may want to get a copy of Cruise Vacations with Kids guidebook (Candyce Stapen, Prima Publishing -- you can get it at Amazon.com). It has suggestions on what to do with kids and teens in many ports around the world. As for the W. Caribbean, I suggest taking a taxi to Seven Mile Beach for lovely swimming and optional rental of water sports equipment on Grand Cayman. Key West has a ton of things to see independently by walking from the pier. They include two museums devoted to treasure found on shipwrecks: Mel Fisher Maritime Museum and the Wrecker's Museum. There's also Audobon's House, Hemingway's House and Harry Truman's Little White House. By Mallory Square is a small aquarium too. The town has plenty of fun shopping and lots of Victorian B&Bs to admire. My favorite spot is Nancy Forrester's Secret Garden which is home to lots of exotic parrots. We had a great time seeing these birds and some were taken out of the cage to perform tricks for us!
Let me know if you decide to go on this cruise.
Luisa Frey Gaynor