You should be aware that a lot of attractions at Disneyland are closed while they build the new Star Wars attraction.
https://touringplans.com/disneyland-resort/closures
You will certainly want to go on the updated Star Tours, the Haunted Mansion is always great, and if you don't have to wait in line too long, Pirates of the Caribbean is fun.
I think the best restaurant in the park is the Blue Bayou (some people prefer the Cafe Orleans, but you can't beat the ambiance of the Blue Bayou. You will definitely need reservations, so make your reservations there before you go, or first thing when you arrive.
If you want to leave the park, you can go to the Napa Rose in the Grand Californian Hotel. Your grandparents can get a glass of wine with lunch there. There are trams, but it is only about a five minute walk from the Park.