We had 13 last week including 8 adults, kids ranging from 15-3, 2 strollers and 1 wheelchair (and a partridge in pear tree). I made 2 dining reservations in advance - they was no charge or credit card required to do so.
My tips-
Big for us - FP runners!! Usually my husband and BIL would be in charge of those. We rode a lesser wait ride, had a snack, bathroom break, whatever and they were back in a flash.
Cell phones - we split up briefly but often. I have older kids, while my sisters have little ones. Often some would do one ride while some did another. Cell phones kept us in touch.
Headcount often- I walked away leaving my 15 year old at a snack stand. It was so crazy with all the little ones, mom in a wheelchair, I literally didn't even notice for 5 minutes and she was calling on her phone freaking out cause she turned around and we were gone.
Snacks - bring some along or you will be stopping every 5 minutes for somebody.
Bathrooms - ditto - try to go all at once or you will be stopping every 5 minutes.
Cameras - everyone take pics of everyone else! We shared our memory cards with each other when we got home. Each captured different things.
Have fun!