Joseph Sjouwerman and Esther Vega married in 1904 in Amsterdam. They had four children, among whom Betsie.
Stadsarchief Amsterdam, archiefkaart Joseph Sjouwerman
In addition, a Jokos file (number 20363) on this family is at the Amsterdam Municipal Archive. Access is subject to authorization from the Stichting Joods Maatschappelijk Werk.