I had a a similar adventure - 1 more day, but a 6 and 1 yr-old in tow. We survived fine.
My trip
My thoughts -
1st day on Oahu - get to Hanauma Bay early (you'll be up early anyway) - we got there at 5:30 and were 4 of about a dozen people in the water for an hour. By about 10-11am you'll be snorkle'd out and leaving just as long lines are forming.
Pearl, Arizona, etc., will take half a day - get there early and be prepared to wait - we toured the submarine next door. Diamond head hike was a few hours, the Dole plantation was fun for kids - another few hours on the way to the North Shore. I suppose Waikiki is a must-do tourist trap, but we didn't get much out of it. Pu Ualakaa State Park was nice for sunset photos. Nuaanu Valley Rain Forest and Nuuanu Pali were a nice few hours. Waimea Falls Park was also a good stop up North, but I don't know if it's still there (well, the falls are still there - I saw them on Lost not long ago - where the pilot ended up).
Maui - Hana is a full day. We left at 7am this summer and the last 15 minutes of winding road were in the dark as we rushed to beat sunset. Haleakala - leave at about 3-3:15 - don't let the "you have to leave by 2a" fool you), and spend a few hours after sunrise hiking the trails. Bring warm clothes - 45 minutes in 35 degrees with shorts and a polo shirt is about the coldest I've ever been - but I had a primo photo spot. I'm been to many of the beaches and Kaanapali is my favorite. Especially Black Rock by the Sheraton, for snorkeling. Sooo much else to do - Ocean Center, snorkeling in many places, zip lines, Pineapple Tour (kids's favorite both trips), Upcountry, drive around the northwest corner.
Kauai - Waimea Canyon, all the way to the end. Napali coast - drive all the way around the north and make the 1/2 mile steep hike. Then take a cruise later. Hit some beaches.
Times are about right. I've been to Oahu once, and probably won't go back. But for a first/only time, you really have to invest the day at Pearl Harbor (at least I did).
Hotels are having deals during this down time. Waikiki was blooming with hotels when we were there (stayed in Ko Olina), so I'd bet there are decent hotels at good rates if you look. Maui, I'd look in the Kaanapali area and not Wailea, having stayed at both. Kauai - not as many choices, but stay south/west to avoid the rain.
The Discovered books are great, but really are worth the effort if you're there for weeks and want to discover the nuances of the island. You should probably just hit tripadvisor and Fodor's web sites for several hours to see what is highly rated and interests you - there will be way more to do than you have time for.