If it were me, and the whole family wasn't into it, I'd find a destination that everyone can agree on. Vacations are costly, and family time is precious......so its very important to us that we all go somewhere where we can have fun together.
Is it Disney that the older two object to, or Florida in general? I ask because there is so much more to Orlando than just Walt Disney World

. I agree.....its amazing and wonderful......but so are many other places in that area that might also appeal to your teen daughters. I have a 16 year old son, and you may want to check out my TR's below (see links in my signature) for all the OTHER places you could visit besides Disney. Discovery Cove, SeaWorld, Aquatica, Universal Studios, and Islands of Adventure are some biggies. The outlet shopping is fantastic. There's Gatorland, Cocoa Beach, airboat tours, and the Kennedy Space Center. Go-karting, mini golf, and International Drive attractions are all good non-park activities that appeal to teens. Dinner shows can be a ton of fun (our teen LOVED the Outta Control Dinner Show in August, as did we). What about an Orlando Magic game? Or a concert at the Amway Center?
Maybe a resort-type property (with some onsite activities....some have lazy rivers, great pool areas, sometimes mini golf, volleyball courts, etc.) would appeal more than a pool home? Many two bedroom units in timeshare properties would easily accomodate your larger family and provide some fun things to do without ever leaving the property.
All that said, we have had equally as much fun on non-Florida getaways as well. Wisconsin Dells was a blast. Niagara Falls is amazing. Anywhere we can ALL go and enjoy together as a family is bound to set the stage for some priceless family memories.
If everyone is into Vermont, then I say give it a whirl. Give the kids some input and have the whole family involved in the planning, whatever destination you choose. If you have to shelf Disney until the kiddos are grown and its a "Dani & Hubby only" trip, then you still have something to look forward to. Their teen years go by way too fast.