True, plus for shows if there are several wheelchair parties, they may limit that handicap seating to just the wheelchair guest, plus one more guest. I know this past May I was there with my mom who uses an
ECV. For several of the shows, we were told that only one of us could sit in the handicap row next to my mom, but the other one would have to find other seating, just below us. This happened at Hall of Presidents, Fantasmic, Bugs Life, and Little Mermaid.
Even though you are talking about WDW and not DLR, the same holds true - for most shows you will be limited as to the number of people who can sit with the person in the wheelchair/ECV, assuming that person does not transfer.
The party limit is 6 (5 plus the person in the wheelchair). Some places as a little more relaxed about this, some are not. Fantasyland in particular is very strict about that number - this is because there can often only be 2 people per ride vehicle, and large parties would delay the ride considerably.
For the few rides which have use the Wheelchair Return Ticket system (8-10 rides in DLR, none in DCA), you will need to have your entire party with you when you go to GET the ticket - you cannot send part of the party nor a runner ahead. My personal opinion of this aside, it is something you need to be aware of.
Be aware that in the Aladdin show, only ONE seat is available for a companion to the person using the wheelchair - the rest of the party will have to find seats nearby or elsewhere in the theatre. Depending on how crowded the theatre is, and which wheelchair seat you go to, there may be room for only one or two people directly next to you in Mickey and the Magical Map. There is also limited space in the Fantasy Faire theatre - only 4 wheelchairs/scooters can be in the theatre and only one spot is reserved next to the wheelchair spot.
In Fantasmic and WOC wheelchair viewing areas, as well as parades (though this is enforced a little less in parades sometimes), only the person with the wheelchair will be allowed along the front. The rest of the party (and they are strict about party size as well, in general), will be asked to stand behind the person with the wheelchair. Sometimes there may be two or even three rows of wheelchairs, and the rest of the party will have to be behind those people using wheelchairs, scooters, or walkers with seats. It is common to see kids sitting on the lap of a person in a wheelchair once they have parked for the show. PLEASE make sure that scooters are turned off and the key removed before allowing a child to sit on a lap during a show. Children will not be allowed to block the view of people in wheelchairs behind you (i.e. I often see kids who sit on the armrests and end up blocking the view of the wheelchair user behind - these children are politely asked to move by CMs). Also, the children will not be allowed to stand up in front of any wheelchairs once the show has started. (I go to Fantasmic a lot, and these are the issues that I see come up frequently).
So a group of up to 5 can go with a person in a wheelchair or
scooter, and the entire party that wishes to ride one of the Wheelchair Return Ticket attractions must be present when getting the Return Ticket. (This is technically the rule, though I have sometimes not seen it enforced)