Glad I was able to help, But I got a little too much Fernald blood in me to be ranked with an angel!!
I think we have some good leads here. I got so involved with Jonathan that I forgot to sum up my investigation of Sherburn and Ira which I will do as I have time. Plus I am curious about George and Jasper ( Martha's son.)
Also I erred on some census data for Jonathan in 1800. His wife Martha should be 16-26 not 18-26.
Also a note on your ancestor Elizabeth Langdon who married William Fernald. Her parents were Tobias Langdon and Elizabeth Sherburne.
They sure knew how to keep a name in the family!
One of my ancestors brothers also moved to Iowa with his family by 1880, Hezekiah Hall Fernald in West Liberty.