According to his "archiefkaart" Barend moved to his mothers address in April 1943, before this date he lived at Amstel 21.
Stadsarchief Amsterdam, archiefkaart Barend Korper
Sophia Vreeland was the widow of Simon Korper (08-12-1892/29-12-1934). She also had a son Philip.
Stadsarchief Amsterdam, archiefkaart Philip Korper
In addition, a Jokos file (number 2807) on this family is at the Amsterdam Municipal Archive. Access is subject to authorization from the Stichting …