In a family file I have Alexander Fothergill, son of John Fothergill and Elizabeth Buck is the husband of Margaret Thistlethwaite. I got this information from the quaker records. She was according to this the second wife , his first being Jane Blakely. John and Elizabeth were Quakers.Perhaps this would help you in your search? I also note that on the marraige certificate of one William Parker of Cam Farm ,William Thistlethwaite is listed as a witness under the title of "relative" on January 10, 1769 ,Cold Cam , Wapentake of Rydale, Kilburn, Yorkshire . Let me know what you think or where this might fit with your people.