Selket said:
For popular rides that you all might want to do together (like Buzz Lightyear, Splash Mountain, Pooh, etc.) you could have everyone in the party obtain Fastpasses.
That is what we did when we traveled with a large party. you can send one of the faster (and most reliable) people in your party ahead to the Fastpass machine with everyone's passes.
The advantage of Fastpass is that you know when you get into the Fastpass line theat you will normally be boarding the ride in 15 minutes or less. It's a very consistent thing. You are never quite sure what will happen with a GAC - there may be an alternate entrance or an alternate waiting area, you may be told to use the Fastpass line or you may be given a slip and asked to come back later.
Plus, all of you will be able to ride together.
If you haven't already, check out the information about GACs (Guest Assistance Cards) in the disABILITIES FAQs thread near the top of this board. It has one section of information about GACs.
The card is usually issued for up to 6; 5 plus the person with a disability. Even with that, there are some atractions where the space is limited and you might be asked to separate into smaller groups - like 1 or 2 people accompanying the person with a disability.
The person using the wheelchair won't need a GAC unless there are other needs that are not met by having the wheelchair. And, as was already pointed out, many atractions have "Mainstream lines" where the lines are wheelchair accessible and people with wheelchairs/
ECVs are waiting in the same lines with eveyone else.
I can imagine having such a large group touring together is like herding cats

but it would help to have some basic touring plans together and ideas of what you want to do.
We had 14 people on our last trip and it was very much like herding cats (I have one cat, but can imagine what it would be like with more).
We had some very specific plans of what to do/see and also had some Fastpasses that my DH had picked up. DH and I and our DDs are very familiar with the parks. Most of the other people we were with were not. It helped to have one person (my DH) leading the group and another person who knew where we were headed (usually me), at the rear to "round up" any "cats that got away from the herd." That actually happened quite often - someone would stop "for just a second" to get a drink or check the price on merchandise we were walking right by. The "herd wrangler" becomes very important to keep the group together.
Having done 14 people this year, 8 a few years ago and 10 on another trip, my best advice is to try to break into smaller groups as much as possible. A group of 6 or 8 is
much easier.
As someone already pointed out, your child's needs might mean that trying to stay together in a large group would be more stressful to him. Even the little things like people becoming hungry, needing a rest or a bathroom at different times mean that a large group spends a lot of time waiting around for others in the group to do something.
Personally, I found it much more tiring on the days when we had large groups together and some of the other people mentioned it was kind of nerve-wracking to them too, since they were constantly having to keep tabs on where the group was.
I would suggest maybe planning to be in the same park on the same day and "mixing around" your groups (just make sure some particular person is responsible for younger children so you don't get "I thought he was with you" "No, he was with you"). It's kind of exciting to meet up with someone and we spent a lot more time talking about what we had done when we met up with people than we did when we were in a large group. It was so much fun to share what we had done with the other people later in the day.
Cell phones are almost a necessity. We had several in each group when we split into groups.