I'm on the Adams side. Can you ask your grandmother if she knows who Harrison's father and grandfather are? It would be great if she knows because I can't find anything other then maybe Harrison's father was Cornelius Thompson who first married Maria Adams (we think) and then had a second wife. There is a story about Maria disappearing...just walking off one day never to return.
Maybe she has picture of the family as well from long ago. Wouldn't that be wonderful!!!