I previously looked at the Cumberland Harrisons, from Yorkshire.There is a William Harrison, of the right age, with sisters named Mary and Sarah, but it does not appear to be the right family, as they, apparently married and remained in Canada. See the "Johnson, Wilson,,Rushton-New England, Canada, Michigan" tree at Ancestry/Rootsweb.
That is very interesting about 1780 being too early for the Loyalist exodus.I still don't totally rely on this information about Sarah being born in Canada because the death records of Sarah, William and Mary in NYC all identified their place of birth as NY. The information the son had was one generation removed, so I'm not sure what it means.
As far as the Harrison's being Quakers, the only thing that I know is that William, Mary and Sarah were Presbyterians, at least from the times of their marriages, until their deaths. As I mentioned, William was married in and buried at the Brick Church in Lower Manahattan.This was part of the First and Second Presbyterian Church. Mary's duaghter, Jane, was married at the Vandewater Street Presbyterian Church in Lower Manhattan. All of Sarah Callender's kids were christened at the Fifth Ave. Presbyterian Church in Manhattan.
Thanks again for all your help and insight. I still have hope of finding something for both of us in the Westhcester Archives, especially since the new information about the Harrisons of Westchester seems to tie in with the Sutton/Sands/Underhill folks we were already looking at.