Louis van Velzen was a son of Isaac van Velzen and Schoontje Grijsaart. He married Sara van Bever in Amsterdam on 30 July 1919, a daughter of Samson van Bever and Sientje Smeer. The couple had three children: Isaac, Samson and Schoontje. Isaac was killed in Mauthausen on 17 July 1942; Samson was killed in Sobibor on 16 April 1943, together with his parents and Schoontje lost her life in Sobibor too on 14 May 1943.
City Archive of Amsterdam, archive card of Samson van Bever and website www.wiewaswie.nl