I'd actually vote sell the prius and pay off the other car with the proceeds. Then you have your "family" car taken care of. You could also sell both cars and buy an older one when you get there. It's hard to rack up tons of miles on an island, so it's not uncommon to find 10yo cars with 40K-ish miles for cheap.
Go to one car and at least one person bike commutes. Hawaii has excellent weather year round, though it rains frequently. I brought my bike during a port visit there, and found between that and transit options, I was just fine. Even when it was raining, I had no trouble on my bike, and frankly, felt like a badass.
Also, since you know where you'll be working (probably don't for your spouse), you could plan to live near the base.
