Having now obtained an abstract of the documents held in Devon Record Office (found by Anne Speight in 2006) that provide the probative link between:
I have updated all of the relevant pages to reflect these facts. Mary Jane Vial's 'Birth and parentage' page has been revised. Two new pages provide as much information as I have about Mary Jane and Sophia's father, Peter de Vial, and their mother Mary Tremlett. A family tree for Mary Tremlett is available to view or download from the File Downloads page.