According to an unofficial guide I have on me (NOW who's sick?), autumn is usually very light when it comes to crowds. That means, even though the parks will close earlier, you'll have much shorter lines, making it easier to get more done in a day. As long as the kids can keep up with their homework, it seems like a great time to go.
I don't know what your budget will be like, but if you want to stay on site, I'd suggest getting at least one annual pass. This will give you access to much better room rates reserved for passholders, and I'm pretty sure one annual pass will allow you to book up to 3 rooms at a time. Perhaps you can get connecting or at least next-door rooms at Port Orleans Riverside. Food court's awesome, and I bet the kids will love the pool there (don't know about the entire age range of the kids, either). You might be able to get away with Park-Hopper Passes for the rest of the group, with the intention of spending some quiet days lounging at the pool, or maybe days at non-Disney attractions like Universal or Sea World. But the money you'll save on room fees will probably more than make up for the added expense of one annual pass. AND if you plan on going to the parks every day, annual passes for everyone! (hey, what do I care, it's not MY money. HAHA!).
I'd also look up some of the free/inexpensive things to do on-property. Trail's End Buffet at Fort Wilderness is one of the best meal deals on the property, and they also have free campfire singalongs & movies every night at Fort Wilderness. When doing meals, think about going for more buffet-type meals, so everyone can really stock up. Like, bagels and cereal for early breakfast, followed by a buffet/family-style late breakfast or lunch, and a fast food dinner. Also see about renting a refrigerator.
If you're not flying to Orlando, rent a van at the airport. All the kids would require a lot of bus shuttle fees, and it might be problemativ getting them all one one bus, and having transportation will allow you to save money on meals off-property some times. If you can't rent a van or other large vehicle, you'll probably save money hiring a town car to get there and back.
Good luck