Thanks,  I was planning on getting a rental car on Oahu so we could go several places.  Pearl Harbor, and The Dole Plantation, Diamond Head for a start.
Also thinking about a riverboat cruise that goes up to a waterfall.  Some hiking on that I believe.
Still have time to figure out what else we want to do.
Oahu has the longest shore time.  Ship doesn't leave until 11pm. So, that is nice.

My life has been at a computer desk.
So hiking, walking, and exercising have never been in my wheelhouse.
But when the weather gets cooler I am going to start walking to try to get my body up to doing it, as I know we will be doing a lot of it.

I understand one's lifestyle is their personal business and I also understand exercise is not in everyone's wheelhouse. So I do not want to offend you, however, you are spending a lot of hard earn dollars on this trip and IMO the last thing you don't want to do is miss a tour because your are not in shape to walk or hike a trail.  Please also remember being in shape will help you in the heat and the humidity and even at the higher elevations. 

My recommendation is begin now but get checked out first by your doctor and begin easy, drink water and enjoy every aspect of your tour.   

My wife and I have averaged about 8 miles a day of walking on our first 5 days of our trip.  I have not been exercising in many many years.  My biggest issue has been sore feet and I have bought some fitted running shoes that I have been wearing.  The fact that I am really heavy probably doesn't help with any good shoe.

So, I would agree that you should get out and do some walking for months before this trip.  Instead of my method of an 11 mile walking day in NYC about 6 weeks before the trip followed up by a 7 mile walking day in Chicago about 3 weeks before our trip.  Probably not the best game plan.