What about this option?
Bring a push wheelchair for getting around at the resort and in non-park places. Rent a scooter from WDW at the parks. At our resort, we will have a golf cart so that will cut down on walking a lot, at least I hope it will.
This would be easier to get in and out of the car. Once we enter the park, we could park our wheelchair and get the scooter. He is also planning on going to the parks on 2 days for sure, not certain he can do more. BUT...what he can do is enjoy the resort and spend the afternoons and evenings having dinner and entertainment with us.
This is basically what we did with my MIL. The scooter rental in the Disney Parks will hold your wheelchair in the back; at least, they did this for us four years ago. I know it's higher priced to rent from Disney, but you never have to worry about taking it apart or putting it together. It's a nicer scooter-better padding, etc. You never have to charge the scooter. If someting bad happens to the scooter you can get a scooter replaced very quickly from Disney. The wheelchair was great to transport my MIL any which way we wanted to do. So, if we took the bus it was okay; if we took the boat it was ok; if we took the car it was ok. This will make it easier on you, too. It's a lot easier taking a wheelchair in and out of a car, etc. It's a little easier on your stepdad, too in that he only has to worry about driving the scooter in the park and not everywhere else. Some of the rental scooters are without lights and at night that can be difficult for some. The Disney scooters have lights. There are park lights on at night, but at night it is more difficult to see.
With
renting a scooter at Disney, you do need to be there early at each park to make sure you secure one (I would say you have the first 45 minutes after opening and you should be ok); otherwise, you are on a waiting list and there's no way to state how long that will take. You do have to wait your turn in line to get one. You pay once in a day, but if you leave the park and want to come back and use a scooter again you need a voucher showing you paid alraedy and that you will be back. You do this for park hopping, too. When you do come back there's no guarantee that a scooter will be available. Again, it's first come; first serve. You do have the wheelchair as a back up in case the scooter is not available. Disney requires a deposit (like a security deposit); so, you will return your scooter to them and not leave it abandoned in the park. Again, you have to wait your turn after a tiring day to return the scooter and get your wheelchair back.
By the way, transport wheelchairs run about $100 to $150 and may be worth buying rather than renting one. That way you can always have one available for stepdad.
There are pros and cons to
renting a scooter in the Disney parks or getting one from an outside rental. You have to decide what's best for all of your family. We've done it both ways and I honestly feel it's easier to rent at the parks, but there's a price you pay for doing it that way. At night, after a long day in the parks I wasn't so thrilled helping hubby put the scooter in the car and then when we got back to the resort taking it out again. We did it to have more convenience at the resort, but you'll have a golf cart there. Also, the responsibility of charging it, etc will rest on you everyday. With it being your first time I would vote for renting at Disney, as long as, you can get to the parks early and don't take too many breaks and come back to the parks later.