There are 2 Residence Inn by Marriott's right in the area. One is in Lake Buena Vista and the other is 2 miles further North by Sea World. With that large of a group, you would need to book some type of suite, but they do have a couple of different levels of suites to choose from. I have stayed in both and would recommend both.
The breakfast buffet is really good. They always have a nice selection of hot breakfast items(eggs, bacon or sausage, pancakes or waffles, potatoes) 5 different types of cereal, milk, juices and a good selection of pastries/danishes. It does get a little crowded during the pre-park rush, but there is plenty of seating outside if you can't sit inside.