I visited this island 3 years ago. It wouldn’t be wheelchair friendly. You would have to take a boat to the island but there are no wheelchair paths leading to and past the beach.
Also due to the tourism which I was apart of but thousands upon thousands would go per year, they shut the beach down until the ecosystem gets rebalanced. Because of the low taxes, Thailand runs of tourism but the reputation is “No Rules” and not clean which brings unwanted tourists that go to party hard.
If you do stay in Ko Phi Phi then it’s split two ways. On the north side of the island, there is beautiful water and it’s for more families or higher end hotels. On the south side, it’s all partying. Kind of like a half-full moon party with pubs and bars. If you are looking for a hotel/Airbnb on the north end then it is safe and relaxing.