We did this a few years ago. I was the parent of the only little kids, so that might have helped me a bit since I was the planner. I did all of the FP and ADR booking (and made sure we were linked in the app, etc). I told folks they were welcome to change anything they wanted individually afterwards but we were the ones doing the initial bookings. We helped with hotels also, but it was up to them to book it. We talked about attractions a lot before the trip, and timelines... (no one could believe how early we had to plan things)...and I had everyone give me their three things they really wanted to do (including restaurants). I worked the plans so everyone's three things would make it into the primary park morning touring plans and FP plans, and there was a "thrill ride" group and a "kiddo" group. (For example, you guys go ride Rock n Roller Coaster and Tower of Terror while we go see Disney Jr).
We also set some expectations - we said we would have a group table service meal per day and a primary park, and that everything else was flexible. That worked well too. We made touring plans, which were rope drop, hitting some headliners, using FP in late morning, and then our big family lunch. After that our kids needed a nap, so it was free time for everyone else. We had plans from 4-7 or so but they were more flexible - sometimes folks came with and sometimes not. There were several mornings where some grandparents were late arrivals. Some afternoons where my brother and SIL kept touring a park we had left. We had some ADRs set up for subgroups to go do things too (like my family went over to Ft Wilderness but the grandparents and my brother SIL went back to DHS for Fantasmic and Sci Fi Drive In).
The thing we made clear was that everyone was free to do what they wanted to, but the group meal and us following our touring plans were non-negotiable. If anyone wanted to spend more time in a shop, skip a ride, come to the park later, etc. we were 100% onboard with that (I would help make their alternate plans if they wanted) but we wouldn't be changing the main plans for it. So if my brother suddenly saw a character he wanted to meet, he could go right ahead, but the other nine of us wouldn't all be sitting there waiting... we would do our next ride and he could catch up when he was done. He could do the ride later during the break or just skip it. It sounds kind of heartless, but it made a WORLD of difference for the trip.
There were still some problems (for example, I had picked a night for Wishes and the Electrical Parade but my parents were tired, they didn't hear me saying this was the only night for it since there were Halloween parties the other remaining nights of our trip, so they went back and rested and then were upset when there were no more nights to see it...).
But overall, having the FP and meals together and otherwise giving people flexibility meant everyone had fun.
I would also remember that things you may think are a definite skip attraction as an adult can be the best things of your trip with kids. For example, we had never done Enchanted Tales with Belle before. Suddenly we go with kids, my daughter ends up being the Beast, and it was one of the most memorable things of the whole trip.
My 13-mo son was absolutely enchanted with the Tiki Room and street musicians, and my daughter with the fountain outside Muppets. And plan that everything is going to take a LOT more time...
Good luck!