You've gotten a lot of good advice already, so I'll just explain things a little more.
Even the rides with alternate entrances, like Haunted Mansion, usually have wheelchair parties wait in the regular ("Mainstream") line until close to the boarding area. Often wheelchair users board at the exit, and there is not enough room for a large party (sometimes 5 people is really crowded). If there are other wheelchair parties waiting, it gets REALLY crowded. That's a problem for rides like Spaceship Earth that have a separate area for wheelchair parties to wait and board. There is a fairly large area for waiting, but then you are taken into the exit area, where there is little space and there is a steady stream of people coming off the ride.
For shows, there are a limited number of "wheelchair seats" for each show (for example, Little Mermaid can take 8 wheelchairs). When there are only one or 2 wheelchair users coming to that show, you will be able to have a larger party sitting with the wheelchair user. When it's "full" for wheelchair guests, they may need to limit the number of people able to sit with the wheelchair user. Sometimes only one person can sit with the wheelchair user. Sometimes that's the way the theater is set up - with alternating spaces for wheelchairs and seats next to the wheelchairs. If it's not busy, you may be able to have 2 people sitting one on each side of the wheelchair. If the show is full for wheelchairs, only one seat is alloted to each wheelchair.
We've traveled with a party of up to 9 and found it's much easier with a smaller party. With a big party, you spend a lot of time just making sure you are all still together and a lot of tim e waiting for someone in the group who needs to use the bathroom or get something to eat. I agree with teri about using 2 way radios and split into groups. You can always meet up later, but it's easier to have several small groups than one huge one.