We often travel with a big group. My best money saving tips include:
1) Except for buffets, everyone just drinks water at restaurants. Saves $2-3 per person per day. You need to agree to get the adults to take the lead on this one.
2) We buy lots of packaged snacks and let people bring 3-4 to the park each day. Some are healthier like granola bars and almonds, but some are pure junk that the kids don't typically get. Park snacks are about $4 each so this saves a bundle.
3) Split meals when possible.
4) Make meals at the vacation house. Our favorites are spaghetti, tacos, sandwiches, breakfast for dinner.
5) Meals off site can save you a bundle. We like CiCi for pizza.
6) Buy bottled water off site or use some type of Britta system. When we stay off site, we always take a soft side cooler filled with frozen waters and leave it in the car. Everyone loves the cold water on the drive back to the house.
7) if you have small kids, shop for little Disney gifts now. The Dollar store and Target often have them. Also pick up glow sticks. Bring these out when waiting for shows and parades.
8) Give older kids realistic expectations regarding souvenirs. Our limit is $30 each. And this money is earned at home before we leave.
9) We don't plan any meals for the last day and just put out all the leftovers. If we don't have enough, we run out for cheap pizza like Dominos.
10) Pack a picnic for the beach day.
I hope you have a great trip!