We are gearing up for our trip to Kauai and Maui in just a little over 2 weeks!!! We're a group of 4 adults. The brother of one in our group highly recommended we rent a 4WD vehicle in Maui for Road to Hana and Haleakala. My boyfriend and I are planning to do a group tour/bike ride down the volcano, but the other couple may drive up themselves as they are not interested in the bike ride. Past that and Road to Hana I don't know how much driving we will do. Is a 4WD vehicle necessary for these things or can we get around fine with a regular car??