I think you should try a group activity on a smaller scale locally and see how that works out before deciding about going to Disney World. This could mean going to a local zoo, for example. Are you near any smaller local amusement parks; so, you could go to one? How about going to a children's museum? I think these experiences would give you a wealth of knowledge and prepare you for a more complicated trip like Disney World. It would help you understand if it's possible for you and your helper to handle a Disney World trip. Zoos and some amusement parks rent scooters. You can usually rent a
scooter from a local mobility store, too but then you have to haul it in and out of car. You may find some or all your kids may not like rides. We have a set of great grandson twins and one is a daredevil and the other one is scared of a lot of rides. You need to find out how this works for you. Usually, we will take the daredevil on a braver ride while someone else takes the other one on a more baby ride or do a show; so, we split up sometimes. Also, with the ages of your children you may find that all of them may not may not meet the height requirement for a certain ride. Some kids don't do well on simulator rides. Getting in and out of rides may be difficult, too. If you can't help it might be a bit much to expect your helper to secure three kids by herself on a ride. Are you ready for a tantrum if one of the children doesn't get do a ride they want to do? What about long waits for a ride? A
DAS is an important tool in your case. But even with a DAS it may prove to be too much to wait in line. If we get back to fastpass for the Disney parks or an equivalent I would definitely use it.
We are in uncertain times and no one can predict when Disney will relax their mask requirement for the parks. Fortunately, your trip is not right now but can your children handle this procedure if it's still being enforced when you go?
Now, you have to realize you will be doing day after day at the Disney parks. The average trek is 6 miles a day. I would definitely try to mix shows and rides and not just do ride after ride. Shows will provide a rest. Right now, we don't know how fast the shows will be returning to Disney. Parades and fireworks provide a rest, too. There are handicap locations for scooters for those activities but you need to be early to secure a spot. Eating at a park can provide a rest, too.
Most important for you is to get identification for each child. There are wrist ID bracelets to use that are not easily removed that would have your cell phone number in case one or more of your children get away from you and lost. In your case I would even try to have a note in a lanyard to describe the child's challenges, too. Yes, they can remove the lanyard but it's worth a try. Maybe, give them a reward for wearing the lanyard each day and not removing it might help them to cooperate.
I would definitely recommend a rest mid afternoon and then go back to the park for the evening. If not then I would consider shorter days. You have to have the strength to handle all of this day after day.
I really feel you have a lot to think about to make this trip doable.