Check out Harpers. Call them and see if they have any large passenger vans or something like that, since it may be your only choice at this point.

Or google "hawaii discount rentals", but honestly, waiting til 2 weeks prior to Christmas to rent a car in Hawaii? This is high season over here.

You snooze, you lose.

Sorry to tell it like it is.
I hope you catch a break.

@:-) Just a word of caution for anyone: whichever place you rent from, on which ever Island, at whatever time, ALWAYS go over the car very thoroughly and document every scratch, dent, ding, etc.