David Cosman was a son of Joël Cosman and Golina van Wien. He was first married to Elisabeth Hamel in 1905 in Amsterdam. She died in 1928. They had two children; Sara (who died at a young age in 1906) and Joël.
Stadsarchief Amsterdam, archiefkaart David Cosman
David Cosman and Betje Serlui married in 1929 in Amsterdam.
Stadsarchief Amsterdam, archiefkaart David Cosman
In addition, a Jokos file (number 15817) on this family is at the Amsterdam Municipal Archive. Access is subject to authorization from the Stichting Joods Maatschappelijk Werk.