William Lyon of Culpepper, Virginia was not a son of John Lyon, 4th Earl of Strathmore and Kinghorne. The earl had ten children and William was not among them: http://thepeerage.com/p950.htm#i9492
I have disconnected William from the Earl.
Also, other family trees claim that William was the son of Frederick Lyon, Min. of Airlie and Isobel Cramond. See https://www.findagrave.com/memorial/122780073/william-lyon for example.
They did have a son called William, but according to A Most Remarkable Family: A History of the Lyon Family from 1066 to 2014 by Michael Hewitt he was born in 35th July 1697 and died as a child on Aug 4 1700. So William Lyon of Culpeper, Virginia is probably not their son either. https://books.google.com/books?id=8c7oAwAAQBAJ&pg=PA81&lpg=...
