1) Make 3 reservations.

On Day 1 rent an SUV or minivan at OGG, which will be large enough for all of you plus your luggage. On Day 2, drop the SUV off and pick-up the convertible at the Ka'anapali car rental depot aka Ka'anapali Shuttle*. Enjoy the convertible all week. On the last day day, drop the convertible off and pick up a mini-van from the Ka'anapali Shuttle in order to transport everyone and their luggage back to the airport.

2) On Day 1, have one couple hire a taxi or shuttle to take them and all the luggage to the hotel. Have another couple hire a taxi to take them and all the luggage back to the airport on the last day.

3) Keep your convertible rental and make another one-day, one-way reservation, on the first and last days. The second car will be the cheapest car available and its sole purpose will be to transport one driver and most of the luggage to/from the airport. Drop off and pick-up the second car at the Kaanapali Shuttle location.

4) Rent a mini-van or SUV for the entire week, and rent a convertible from the Ka'anapali shuttle only on the days you plan to take long drives.

*I know that Alamo and National have a presence at the "Ka'anapali Shuttle" location, which is near the Kaanapali Beach Club (former Embassy Suites) building. I'm not sure what other rental companies rent from this location. Also note that this location has limited hours, so you have to plan your pick up times around their schedule:

National Rental Car Ka'anapali Shuttle Hours: Sun-Sat: 07:00 am 05:30 pm