Hi Kevin! As a grandparent myself I know that being with the grandchildren and watching them enjoy the magic of Disney is just as important as anything else. Seeing them experience something for the first time is priceless.
Although the grandparents might not want to participate with the attractions they might be pleasantly surprised at what they can enjoy. The parks are not full of just thrill rides but instead have many wonderful shows and calm attractions that grandparents all love to participate in. Check out the
Park Attractions and go through them and I think you will find many that they will enjoy and that you can do as a family.
Some that come to mind that are not to be missed by all include: Philharmagic, Wedway People Mover, Riverboat, and much of Fantasyland in the Magic Kingdom park. Spaceship Earth, Imagination, Frozen, and Turtle Talk With Crush in Epcot. Great Movie Ride, Muppet Vision, and Toy Story Mania in Hollywood Studios. Safari, Lion King Show, and exploration trails in Animal Kingdom.
As you can see there is quite a bit to see and do for all ages in the parks. Therefore, Disney does not offer tickets that vary the experience for the guests. Each park has a daily ticket for all guests that allows them to ride the attractions, enjoy the shows, and experience all the entertainment. I am sure they will find it well worth their time and money to be in the parks with the family.