Our f irst trip to HI was in 1998 with Perillo Tours. It was an 11 day trip to three islands. I think that would be a bit much from what you say about your parents.
I would fly them to Oahu. I am taking my granddaughter the end of March. I have booked guided tours where we get picked up at our hotel for each thing we are doing: Polynesian Cultural Center; Arizona Memorial; parasailing; a taxi to our luau and the kahala hotel dolphin experience and a shuttle to the aloha stadium swapmeet. If you want them to go tothe PCC you can book, like I did, the Ambassador package which include a guided tour so they don't miss anything, excellent seats for the show there, and they have handicapped vehicles for those that need them (either wheelchairs or scooters). Dont' know if that's what you are looking for, but just to let you know, my husband was 72 when we first parasailed in HI so don't give up on the old folks, lol