Joel Zwaab was a son of Emanuel Zwaab and Duijfje Komkommer. He married 1 July 1915 in Amsterdam to Rozette Blog, a daughter of Gompel Blog and Netje Visschraper. The had a son Emanuel.
City Archive of Amsterdam, archive card of Emanuel Zwaag and family registration card of Joel Zwaab from the Municipal Archive of Den Haag.