I went on a large family trip a few years ago, and noticed the following:
1) If people are a pain in the you-know-what normally, they will also be that way at Disney (and sometimes, because of the atmosphere, they are worse than usual). Don't let them ruin the trip for you.
2) Don't force everyone to stay with the group 100% of the time. Get together for a few rides, a few meals, but in the end, just let everyone go do their own thing.
3) If you happen to be the couple with no kids yet, nobody cares about what you want to do or say. This is somewhat unfair (we paid a lot of money, too!), but that's just how it goes. As I said before, don't be afraid to separate from the group and do your own thing, every once and a while
4) Some people take way too long to get ready in the morning. If you need to be somewhere by 8am, tell everyone it's 7am. lol
Good luck

We are doing a solo trip in May, and are very glad it's not another giant group. lol