Ahoy, Robin!
Your Disney Dream cruise is just around the corner, and I know you cannot wait to get onboard to experience this ship! I hope your daughters will check out
Vibe, which is just an amazing space for teens. They'll especially love the deck area with their own pool and smoothie bar. I always recommend going the first night because the counselors are there to help with icebreakers and getting to know you activities. My teenage daughter enjoys everything about the programming-the friendships, activities and interacting with the coolest counselors at sea.
There are areas that are adult-only on the Disney Dream, and the Senses Fitness Center is one of them. I wish I had better news, but even with your supervision, your girls will not be able to use the facility. They can still stay shipshape while onboard by running around the track on Deck 4 (a lap is .4 of a mile so eight times around is equal to three miles). Goofy's Sports Deck offers a basketball court, and I've seen soccer and dodge ball played there as well. Another idea is to participate in the Castaway Cay 5K when the ship docks on Disney's private island. You can sign-up for free on the ship prior to arrival (minimum age is 10), and March is typically a great time to participate because it isn't too hot. You'll receive a runDisney bib and an adorable Castaway Cay medal as mementoes from your experience!
I'm sorry your girls won't be able to utilize the gym on your sailing, but there are many ways to be active while at sea like I mentioned above and don't forget
Port Adventures! Have a look around at the offerings for the Bahamas, and I'm sure you can find some great options.
It was a pleasure assisting you with your question. If we can help again, please let us know.
Nancy