Willem was the son of unknown parents. The date and place of his birth have not been found.
His wife was Katharina von Montfort, who he married in 1442. The place has not been found. They had no known children.
Note 1
Jacob Jansz., d. Abt 8 Oct 1461-5 Dec 1461 & Lysberth Symonsdr. van der Burch