Dawn,
I apologize for not responding to your questions earlier. I think you've gotten the info you need from others, and I think you'll be glad to have rented the ECVs. My only concern since you are staying off-site is the need to disassemble and reassemble the carts. In our collective opinions they are very heavy even when taken apart piece by piece. Please make sure that you have someone with you who has good lifting capacity (it's a lot harder to get 40lbs. from the ground to the trunk than you would think). We tried to take it in the car with us once, but no one in our group was able to comfortably lift the parts into the trunk (bad backs, injured or too young). If you can lift the pieces into and out of the trunk you'll be fine. The other option is to check with your hotel to find out if their transportation to the parks will accomodate guests in wheelchairs or if they can recommend a way to get your family and carts to the parks without assembling/disassembling twice or more times a day. Since we were on-site my Mom was able to drive the ECV right onto Disney buses, monorails, boats, etc. with no problems. I don't know what your situation is, but if at all possible you may want to look into staying on-site. We stayed a couple of days at ASMo and they were wonderful to us. We didn't have to worry about first floor accommodations because there are elevators in every building. They also lent us a regular wheelchair (after leaving a cc deposit) for the week that we used to go to dinner and shopping.
Best of luck to you and happy planning!
Patti
sweetp0618