Pete, a must see and lots of fun in Boston is the Duck Tours ... they use WW II amphibious landing vehicles to tour Boston ... both on land and on water. I really don't know if they are handicap accessible, but the web site is
www.BostonDuckTours.com
Hope you enjoy your tour of New England. We have lived here 24 years and we love it (most of the time). Newport mansions are a real treat, as is seeing the town itself. There are bus tours too. I think if you did a search of Newport RI, you could find lots of information. We stayed in a B&B and had a great visit.
In Boston, if you enjoy pasta, don't miss the North End. We try to get down there once or so during the good months and walk around and then try one of the great family-owned Italian restaurants ... always a treat.
Have a safe trip.