Source S-19 Title: The Scots peerage, founded on Wood's edition of Sir Robert Douglas's peerage of Scotland; containing an historical and genealogical account of the nobility of that kingdom, Vol. VI Editor: Sir James Balfour Paul. Publication: D Douglas in Edinburgh 1909. Available without charge at [Open Library]
It may be possible to confirm family relationships with William by comparing test results with other
carriers of his Y-chromosome or his mother's mitochondrial DNA.
Y-chromosome DNA test-takers in his direct paternal line on WikiTree: