Izaäk Simon Bollegraf was a son of Simon Izaak Bollegraf and Hester de Beer. He was already married in 1901 in Groningen to Sophia van Gelder, who passed away on 6 August 1939.
On 17 August 1940 he married again to Rosette Hoffmann.
City Archive of Amsterdam, archive card of Rosette Hoffmann, websites Alle Groningers.nl and www.wiewaswie.nl.