It would really be worth it to research the Islands, there is so much to see & do. It depends on what you two like. Each island has it's own beauty, activities and sights.
You could go snorkling, even if you can't swim, I did & you can stay close to shore & still see fish & coral. On Kauai is the "Grand Canyon of the Pacific", beautiful waterfalls and a boat ride to the Fern Grotto.
The island of Hawaii has some great historical areas, the place where Captain Cook came ashore, a green sand beach which is the southernmost point in the US, some beautiful black sand beaches & Akaka Falls, horse country, the drive through volcano, Thurston Lava Tube.
Oahu has a lot of great scenery and of couse Pearl Harbor. There's so much to see & do. It's a beautiful place.