Doyd, I would urge you to consider borrowing a scooter or lightweight manual chair from the NMSS's lending closet. I also encourage you to get one for a full, random week well before you go and decide if you'll be just as happy borrowing a comfortable manual chair from them.

A couple of advantages with the manual:
-you're bringing plenty of pushers
-easy lifting, no dis-and-reassembly issues
-no charging (or batteries pooping out in the middle of the day)
-fitting into a vehicle
-the ability to get up and push it so you can stretch without the scooter's power being wasted while a kid uses it like a go-kart
-much easier to fit in a shared hotel room
-it's quite a bit less complicated if you're not accustomed to using one at all times
-much less chance of airline damage

I would also strongly encourage you to borrow from your local chapter and take it with you throughout the trip, you don't want to spend a bunch of time in that zoo of a city trying to find locations to get and return it. Also, you can quietly make your reservation with the society and avoid the expense and competition for them in that area.

Whether scooter or manual, borrowing from the society is free. You should make your request at the earliest possible date.

I have done all the Disney parks with both my manual chair and scooter and while the scooter offers more independence, the manual is a much simpler experience if there is someone willing to push it.