First, let me say I live in Crawfordsville, IN. We have driven to Disney World many times. We have flown there, too, but not with a wheelchair at hand.
I'll start out by saying Disney's POP Century resort is my number one choice for values and I, too like it better than the moderates. I've been to Disney World over 40 times through the years and we've tried most of the resorts. For $15/night more you can get a room upgrade for a better room location at the values and I highly recommend doing it. The preferred room location will get you closer to the buses to get to the parks every day. You are closer to the food court, too with this preferred room location. You need to select this as an option if you are using the Disney website for booking or tell the
travel agent you want this option if you do it that way. Also, I would plan on a slightly longer trip. I would add one or two days to the Disney trip to compensate for the shorter days at the parks which I highly recommend doing there for all concerned. If you are using a car the room location becomes less important.
I pushed my mom for the last 5 years on trips; she passed away at 91 years old this past July. We went twice to Disney World during that 5 year time period with her in a wheelchair. We drove both times to Disney World. I managed doing it and I'm almost 60 years old, now and I'm not an ideal weight myself, but I managed. My husband used a
scooter for those trips; so, it's very comparable to your situation. First, you need to realize that long days at the parks will not work well. We did breaks in the afternoon with naps and went back and forth each day for a longer day at the parks. For the AK park, we went the whole day (left after the parade) and did not come back and forth to that park. I didn't need a nap, but my partners did need one. Your parents sound younger than my bunch, but it still may be a good idea not to overdo at the parks each day. We averaged 8 park hours at the parks with a mid day break. We did a loop in each park; so, we saw the whole park. Avoid at all costs not to back track through the parks.
You strongly need to consider getting a lightweight, portable, travel wheelchair. On sale, you can buy one for $100 to $125 (without tax). Our wheelchair went 15 pounds and I managed with it. Some wheelchairs can go up to 50 pounds. One year we did my MIL in a 35 pound rental wheelchair and we felt the difference. At the time of her trip hubby and I shared the duty of pushing the wheelchair. She weighed more than my mom, too. I'm not sure you can rent a lightweight wheelchair; so, I would buy one. It may be useful (hopefully not) in the future, anyway.
Next, I alternated activities at Disney World. We would do a ride, then a show, then another ride and another show, then we would eat and do a ride again. This allowed me to rest with pushing the wheelchair all day. I was very determined to make it work for us. I was determined and I had the endurance and will to do it.
In my mom's case she never left the wheelchair at Disney. She could use a walker at home. We did the rides where she could stay in the wheelchair. The only exception out of the wheelchair was my mom did go on Soarin' at Epcot in The Land Pavillon with our help. Anyway, this means we didn't really do any thrill rides. Both trips we went during the Christmas season for two reasons: more shows to see and it's cooler in Florida in November and December. Also, there's less rain in those months. I strongly recommend you give this time of year a consideration. The Christmas season is very special at Disney World. You have the time to change your mind about the time to go. The Food and Wine Festival is fun, but we still liked the Christmas season better. Each park has their own special activities for the Christmas season.
If you are using a car for your commute to the parks, you need to remember you will have to have a car that will hold a wheelchair and a scooter. This assumes you are renting off site equipment for your needs, here. Offsite rentals are much cheaper. Also, you will probably need some help getting the pieces of the scooter in and out of the car. The base of the unit is where two sets on hands can help. If you will be using Disney transportation (buses) at a value resort you may have to wait a while for your turn with two vehicles that need the handicap spots on the buses. For the Disney buses, you are allowed on first to get positioned on the buses. The scooter needs to be locked in and you need to place the scooter in the proper place on the bus. You may have to help your dad and get the scooter in position yourself. In your case, I would get your mom situated first on the bus; so, you will be free to help your dad. You are last off the bus; every one departs before the bus driver unlocks the handicap vehicles. Having a scooter at the resort will help your dad get around there, too.
When renting an off site scooter you are responsible for charging the battery every night. You don't want to get stuck at the park with a scooter that doesn't have enough juice to run. There's a meter/guage you can watch to make sure the scooter is holding it's charge. I recommend bringing your scooter battery charger with you to the parks in case you need an emergency charge. To conserve your battery power your dad needs to remember to shut the scooter off during shows, parades, and fireworks. You will probably have to remind him most of the time to shut it off when standing still. Take the scooter key with you when he's off the scooter like with eating in the parks. Without a car, you need to get the scooter and wheelchair in the room with you. With a car, you can charge the battery of the scooter off the scooter with most models that are portable, travel scooters. Most batteries go about 30 pounds.
I would get your dad use to using a scooter ahead of time. You can practice for free at the stores with their scooters. Those scooters are more awkward and bulky, but it will help to learn about the scooter beforehand. You can practice with an offsite scooter rental at the resort before you get to the Disney parks, too. In your case, I would strongly recommend going to a local zoo where you can rent a wheelchair and a scooter for the day. This will give everyone good practice. A zoo is still easier than Disney World. It's so crowded at Disney and you need to learn how to manuever the wheelchair and scooter down and up the handicap ramps at the parks. You don't want your father jumping a curb with his scooter. This is especially hazardous at the MK park. It can be so crowded that you can't see the sidewalk ramps easily.
With regards to costs maybe you can get gifts from now until the trip that would defer the costs of the trip for buying a wheelchair and/or staying a few days longer there. Try to get a Disney trip with a
free dining promotion or at least a good discount on the room. Disney will run promos; so, you need to watch for those times and book in the window for the deals. There's no guarantee there will be promos, but just keep it in mind.
The look on my mom's face when she shook hands with a character was priceless and worth everyday of pushing her in a wheelchair. I miss those moments, now.
If you have any other questions, feel free to ask.