we will have between 8-11 people?
If the person in your party has a wheelchair and no other special needs, they will not need a GAC. The Guest Assistance Card is a way to let CMs know about invisible disabilities that need accomidation. If the only needs are mobility or to have an accessible entrance, then having a wheelchair or
ecv will be all you need and you won't need a GAC.
They usually will give a GAC out only for up to 6 people (5 plus the person with a disability). They may give it out for more under special situations (decision of the CM in Guest Services)- like if there are a lot of children who would be in a party by themselves otherwise.
For things like parade/fireworks viewing and shows, there are a limited number of wheelchair accessible seats or space. So, they may limit the party to even less than 6. When it was busy, we've been limited in the Illum9inations viewing spots to 2. This is whether you have a GAC or not, just because of space.
For example, for shows like Little Mermaid, American Adventure, Indiana Jones Stunt Show, ITTBAB there are empty spots to park a wheelchair or ecv with a few seats near each spot. For those, they usually ask that the rest of the party either choose a seat somewhere else in the theater or in the row ahead of the wheelchair spots.
For some rides where wheelchair/evc users board at the exit (usually after having waited in line), there is limited space at the exit for people to wait, so they would probably ask that only a few of your party board there. In Haunted mansion, you end up missing the Shrinking Room if you need the accessible entrance, so you may want to only have a few in your party use that way.
If you are able to go to the parks early and use fastpass, you may find that you don't need a GAC at all. Early in the morning, you can get on a lot of rides with very short waits. Even some of the rides with long waits at one time of day, may have a very short to no wait at all later that same day.