Families grows... and things change... just embrace it. ( just wait till they get married, and then you have grandkids...so much fun )
I would suggest that you ask them what they would like to see or do. Maybe a behind the scene tour, there are quite a few that they might enjoy.
Water Parks, pool days, mini golf, Fort wilderness activities.
Head to Disney Springs, balloon ride, dine in movies/or regular movies, bowling, check out all the music and entertain options in the evening.
You could do a day or two at Universal, and Island of Adventure.
Head over to Coco Beach for a beach day and hit up Ron Jon Surf shop our friends just did this before heading out on their cruise, and the grand-kids just loved it. They got shirts and board shorts, that were 'way cool".
Cape Canaveral great way to spend the day.
I think personal space really starts to play into the picture around this age. So maybe a family suite so they don't have to share a bed, and everyone can kind of spread out. This worked really great for us when we would have both DD's. Having a extra bathroom with teenager is a plus, that child you could not get to brush their hair, or could have cared less about matching clothes.... now is spending hours in front of the mirror and getting dressed... girls and boys alike.
We also like TS service with them, it would give us a chance to eat as a family... and listen to them... You can find out alot of stuff about your kids when your eating dinner and they are distracted with food... they will just talk and talk... Plus it's a teaching moment for them and they don't realize it, trying new foods, manners, ordering, even paying the bill. We taught our DD's about paying the bill, tipping and how to read the bill and handle if the bill is not correct... They thought it was cool to do it, they were both nervous at first but after they practiced a few times it built their confidence up.
You could let them be part of the planning, maybe each one planing a full day they are the leader that day from start to finish, but on there day they have to be in charge. Let each one pick out somewhere in the world showcase to eat that is a bit different than your normal go to spots. I suggest a meal that has some type of entertainment, Teppan Edo, or in Germany with the band, Coral reef with the aquarium was/is a family favorite. Sci-fi at DHS is another one the DD's loved, they could not believe that when we were kids we had actually went to the Drive Inn to see movies...
Be on the hunt for hidden Mickey's ... or some other kind of scavenger hunt....