Wow, that can be a tough one. It sounds like you are sharing a room, am I right? My first bit of advice was going to be get two rooms so everyone has a little space.
We haven’t been to WDW w/o friends or family since we got married. I love to share it with other people. Last summer we went with a group we hadn’t traveled with before and all went well, not a single problem. In fact, we have never had a issue come up with a group we have traveled with.
We pick a meal each day so we don’t stand around every day trying to decide where to eat. I have a rough idea of what park we are going to each day and write that down, once we get to the park I just go with the flow. Everyone has to be patient and willing to work together to make it work.
Have a meeting with everyone going and allow everyone to help in the planning. Make a list of one or two attractions in each park that are a must do for each person and that’s what you do when you get to the park. That way no one can say that they didn’t get to do what they wanted–they got to pick their one or two important rides.