Hi Kathryn!
Welcome to the Disney Parks Moms Panel! My family and I just returned from visiting Walt Disney World Resort with my parents who are 70 years old! My mom also has trouble with her knees, so I understand you wanting advice on which attractions are most comfortable for those Guests young at heart!
My mom found it challenging to get in and out of the attractions involving boat rides. She was still able to go on them, but needed assistance entering and exiting the boats. My parents had no troubles entering and exiting their Doom Buggy in the
Haunted Mansion, clam mobile in
Under the Sea ~ Journey of The Little Mermaid and the emission-free vehicles of the Tomorrowland Transit Authority PeopleMover during our days at Magic Kingdom Park! Your in-laws might have a blast on
Toy Story Mania! at Disney's Hollywood Studios and will love to explore the history of communication on
Spaceship Earth while visiting Epcot.
In order to board many attractions, you'll need to step onto a moving platform. If the platform is moving too quickly for your in-laws, just ask the Cast Member helping Guests board to slow down the speed of the platform. They often slowed it down for my mom, allowing her to take her time getting in and out of the vehicle. Also, if your in-laws need to take a break from walking, there are
wheelchair rentals available, too!
I'm wishing you and your family a magical vacation!
Beth