Oh yeah, I've been there too. My family relied on my Disney expertise too, but they were resistant to getting up early, and establishing a touring plan. They didn't want to feel "constrained" by ADRs! So we'd end up getting there at ten, in the middle of the crowds and long lines everywhere.
Then they would turn to me and say "well you're the Disney expert, what do we do?" I finally got mad enough to say "turn back time so you can follow my advice in the first place."
But I digress.
Compromise, courtesy, and lots of time apart are the key ingredients for a multi-family vacation. Maybe you could all meet for breakfast and choose the same park to visit each day, but split up inside the parks to do your own thing, and meet at lunch or for the parade. Another option is to give each family unit a chance to choose the days activities.
The number one thing that caused our family strife was feeling like we all had to be together all the time. Especially the person who was bankrolling the trip (my sister) - she really felt that since she was paying for our joy so to speak, she ought to be able to see every second of it. Except there wasn't any! I really had to make a point of acknowledging that I loved and appreciated her for giving this trip to all of us, but at the same time pointing out that our interests were so diverse, that none of us were having a very good time sticking all together. The little ones were cranky, the older kids were bored, the adults were tired, etc.
Once I was able to convince my group that it was okay for us to split up throughout the day we were fine.
After that point, my family would just get up early and hit the parks, meet everyone at lunch, and bask in their awe at all the attractions we had already seen.
We made sure that we always had at least two meals together each day, and with cell phones we were always able to call each other and arrange meetups.
Good luck and have fun!
