You definitly don't need a rental car - as the poster above noted the shuttle will take you between all three hotels. I think Hotel Lanai guest also have access to many/most of the amenities at the Starwood properties. The golf at the Lodge is fun - you can also rent bikes, go horseback riding, skeet shoot, snorkel, etc. There are several nice hikes to do - the hotels usually have maps or one or two.

If you decide to rent a jeep for one day to do some exploring (the cars have to stay on the 30 miles of paved road) don't rent until the day you plan to use the jeep. Cancellations are not allowed less than several days in advance, and rain makes many of the dirt roads impassable even in a jeep. Jeep run, I think, about $150 a day - there are two rental companies (the hotels have information).

I liked Lanai - undeveloped, enjoyed doing several hikes, hanging out, etc.

Have a good trip.