We always seem to travel with a large group, although not quite as large as yours. But here are some things we have found when travelling.......
We are the "matching shirt" family.

We try to have matching shirts for every day of the trip. Some of those shirts are the $5.00 Old Navy t-shirts from 4th of July, some are Disney shirts, some are just a plain solid color shirt. Back in March, we put the kids all in tie-dye shirts. My point being is that when you have a large group, it's soooo much easier to find and spot people when you all have on the same color and you're not trying to remember who was wearing what. You could even make up some fun Family Reunion at
Disneyland shirts ahead of time. And we always take a group photo each day.
Oh, that reminds me.....back in Nov. 2004, we went to WDW (did the Grand Gathering too!) and we all had on long sleeve black t-shirts. On the front left chest, it said Orlando 2004. On the back was a large skull & crossbones and underneath it said : The NEW Pirates of the Caribbean and then all of our names were underneath that. We got ALOT of compliments on them!
For us, instead of renting multiple hotel rooms, we rent a house nearby. We find them on VRBO.com. We are renting a house in a couple weeks and I think it's around $250 a night? can't remember now...... Anyway, for 7 adults and 5 kids it's very much worth our money. We are able to cook breakfast, pack lunches & snacks to take in and then come home for a hot meal. We found that if we ate out every night, we'd be facing a $200-$300 bill. So it was much more economical to eat in. Plus we have the benefit of a washer & dryer which is a God-send with young kids!!!! Obviously you won't find one house to fit all of you but maybe you could pick your favorite people to room with and the others could find hotel rooms?
There is no way you can get everyone to do the same thing at the same time, so maybe plan a few scheduled events ahead of time like Disneedee said. Set one meal aside to do a character meal together or ?? Maybe set a certain time each day, like say every day at 11:00 everyone meets in front of the castle to re-group and check-in. Everyone will have their own "plan" and if you can try not to control it all (something my mother has not yet mastered!

) it will be a much more enjoyable trip for everyone.
That's all I can think of now....I'm sure more will come to mind later!