Does anyone visit Religious Society of Friends (Quakers) • Friends House, 173 Euston Road, London NW1 2BJ ? There is a compilation there http://quaker.adlibhosting.com/Details/fullCatalogue/46413 that could shed light as a potential source for the parents of Robert Willson as documentation found as unsourced infers his parents were Stephen and Sarah. The unsourced evidence would imply that Sarah was only 15 y/o when Robert was born. This same source indicates that Stephen and Sarah married on the same date as sourced for Robert and Ann's marriage? Many Quakers were immaculate record keepers and this could assist in extending this lineage.
Thank-you!