saw your post about Disney, we have been going for years. Here are my suggestions:
sun screen and big floppy hat or ball cap if you're a guy.
Take and or suggest snack breaks - that's good for a 15 minutes rest.
I sit when ever possible.
I don't go on all the attractions: so I sit in the shade and wait for everyone.
You're young so I don't know how this would go.
We rented a wheelchair one trip and my son in law had a ball pushing me. You all could take turns in the chair.
Just don't rush about without a plan. Look at the list of attractions and plan your route. Suggest that you each list the attractions you want to do and blend them all togther. Go from point a to b to c to d to e; don't go from a to d back to b then e and c, in other words plan your route and suggest you all take your time so you all can really enjoy your day.
Hope this helps