There aren't that many guide books for the Isle of Wight however if I were to buy one I would probably opt for the Rough Guide to Hampshire, Dorset and the Isle of Wight.
I have always driven on the island as it's so much easier for us to take the car over although I have travelled on foot on one occasion for a pub crawl and I took the hovercraft over. Train coverage is relatively poor there however the bus network is quite good. If you're looking to explore the island and investigate your husbands ancestral links then I would opt for a car.
There are many options for accommodation. I can't recommend any in particular as we've always gone over on day trips however I was looking at a long weekend a few weeks ago (we ended up going to York instead!) and renting a cottage was our preferred option. Homeaway and Airbnb have plenty of choice.
I would recommend this site: https://www.isleofwightguru.co.uk as there is plenty of information on there written by, I assume, a local.
There are quite a few English Heritage sites on the Isle of Wight so if you are interested in visiting them then it may be prudent to purchase an overseas visitor pass, likewise the National Trust.