No, you can't get everyone to agree on everything all the time but...... Aren't you going together to be together? It's work but you need to plan and discuss and plan and discuss again. Everyone can have input on the plans; so, noone has to take over. Find the rides and shows that everyone wants to see and then do those activities together. Park schedules can help you with the times of the shows. Sometimes, mini-groups work better if there are varied interests and ages but at least you can still have smaller groups together rather then no group at all. Set times for all meals and pick the places in advance; so, everyone can have a schedule ahead of time. That way, everyone can meet at those times or skip it if they are enjoying other aspects of the vacation. You're not forcing anyone to be together but giving many opportunities to be together. Radios, cell phones, and hotel room phones are great ways to communicate. Use them all.
If you find nothing working on the together plan then accept the fate that everyone is so different that it's best to go your separate ways. It's miserable if you keep trying and all attempts fail. My final plan is not to over plan. GOOD LUCK!