I think it is sweet that they want to spend time with their family. Since this will not be your families last trip to WDW, why not try to be accommodating and modify your trip to spend more time with them? I would not expect them to spend a lot of time in the parks. What I would suggest is to change your resort to one that is more senior friendly like maybe Gaylord Palms? If you want to stay on site, a resort large enough where they will not feel confined to the room and can sit/walk inside the lobby. Even a cabin at Ft Wilderness would be accommodating and they could prepare meals while you are at the park. When we took my parents to our cabin for our ski vacation they would come watch the kids tube at the slopes for a few hours, then they headed back to the cabin and had dinner waiting for us when we returned. Another benefit to the cabin is parking right at the cabin. Many seniors enjoy the cabin an evening activities and you can drop them off where they need to be in the car and then the driver circle back to park and then join the group.
I wouldn't expect them to try to walk an entire park but meet up with you for maybe dining reservations, a parade, Fantasmic (because they can sit vs stand). If you do a character breakfast, maybe see a show, then they head back to the hotel while your family rides or roam the park for a while. Maybe not spend as many hours roaming/riding park as you normally would. There are plenty of other things to do in Orlando and WDW that wouldn't require they walk as much as inside a park.
This may not be your ideal plan, but it might be the last family vacation that they can attend.
I wouldn't expect them to try to walk an entire park but meet up with you for maybe dining reservations, a parade, Fantasmic (because they can sit vs stand). If you do a character breakfast, maybe see a show, then they head back to the hotel while your family rides or roam the park for a while. Maybe not spend as many hours roaming/riding park as you normally would. There are plenty of other things to do in Orlando and WDW that wouldn't require they walk as much as inside a park.
This may not be your ideal plan, but it might be the last family vacation that they can attend.