LOVED your perspective!! I have been watching this thread because I am planning a trip that will likely include grandparents.
Been having the onsite/offsite debate especially since we can only afford a value room. That said, onsite sounds easier since folks can split up and go back and forth between room and parks at their leisure without having to wait for 1-2 cars. Plus, we can get free dining, which I think makes paying for food less complicated.
We do want to move slow with plenty of breaks - especially since we will have a 3.5yr old in our group. The space of an offsite would be so nice!
Issue with the value rooms is they really aren't built for hanging out with family time. They are massive structures themselves as well. Just getting up and going for coffee in the morning is an exercise, especially for those with a silver-hair status.
I know ASMo has family suites that offer a bit more room and a small kitchenette type (minifridge/coffeemaker/microwave). You can do connecting rooms which also gives the illusion of more space. But really the Values are built for park commandos on a mission.
Have you considered doing something like DVC point rentals? Get into one of the DVC timeshares and pay Moderate prices. You won't get the free dining option from Disney but you can at least have a much nicer room. Nothing beats having your own kitchen and laundry, especially with a 3.5 yr old in the party.
I'm biased. We visited Disney once and stayed in All Star Sports. Did 5 days of park commando as a family of 9 adults + one infant. When we returned to orlando we stayed in a very nice offsite timeshare. Now I own DVC and Marriott timeshares. I just won't go back to staying in an ordinary hotel room. I need my kitchen and laundry. I gave up staying in a DVC studio too. It's a 1bedroom unit or else.
Perhaps you and your parents could split the cost? Pick one of the resorts that offers the best mix of resort appeal and park convenience. Boardwalk and Beach Club offer the best proximity to EPCOT and DHS. Just a short ferry ride to each (or a short sprint walk for you commandos). Bay Lake, Poly and Grand Floridian each have DVCs with an easy monorail or ferry ride to MK. Bay Lake has some of the best views of MK, especially at night. Animal Kingdom Villas is great for making your resort the place to meet. You wake up to a safari of animals at your door. Saratoga and Old Key West are more removed from the action. Buses to the parks but ferries or walkways to Disney Springs. We love Saratoga for it's nice scenic walkways around mini-lakes.
An offsite resort does make splitting up harder. You have to provide your own transportation which always seems to create arguments over who's ready to go. I guess you could rent two vehicles: one for you and one for the grandparents. Then I'd probably pick things like meals and sitdown activities to meet up for. Like meet at Crystal Palace for lunch with Pooh then spend a couple hours doing FP+ together. Group your FP+s in the same general area so you reduce the crisscrossing. Like Peter Pan, followed by Mickey's Philharmagic, followed by Winnie the Pooh. Throw in a ride on Small World and the Carousel as time allows. If you make good time, you might even be able to do Little Mermaid together. If the grandparents are up to it, swap out one of those FP+ for Seven Dwarfs. You get a ride photo and video on Memory Maker. Very cool keepsake since it captures both stills of you on the ride together and a slow mo video of your reactions going down two of the hills. (I cannot ride it myself, but I've arranged for my family to go on it together multiple times. Including my 80-something dad and his 80-something brother.)
If you do an offsite resort, make sure you leave time to just enjoy the resort a day. Maybe post cruise. Half breakfast in the room together. Hang at the pool together. Have dinner together. Do all your cruise laundry.
I'm gearing up to bring my family down for another long weekend trip but to Universal and SeaWorld. I want them to stay offsite with us, which means they'll have to rent cars. We have some experience doing that when we vacation in Williamsburg, VA together. I get multiple apartments so everyone has a bed and we meet up daily. We'll go to Busch gardens together at least one day, then we go in different directions. Sometimes we hang out at the pool together. We do a family cookout one night. And we gather just about every night to play card games in my apt. Last summer it was 11 people sitting around the dining room table playing cards. The others would drop in and out bringing treats or just to see what was happening. My nieces and nephews LOVE these family trips.
Bottomline, it sounds like your parents want to share some of your love for Disney. They're probably being a bit unrealistic about their stamina for Disney, but don't let yourself pass up the opportunity to share the memory together. YOU ill be going to Disney many times over the years. No amount of rides on Splash Mountain will come close to being as special as seeing your child having fun with the grandparents while in the shadow of Cindy's Castle.