Abraham ('Bram') was a council communist. Emmanuel ('Manie') Korper, also a council communist, was his brother. Bram's wife Rosa Reens (1892-1928) died in childbirth. Her son Rudolf Herman was then raised by Bram's sister. Bram committed suicide, just like Manie. Their sister Sara survived the war.
There are pictures of Bram and Manie at the IISH, Amsterdam.
Lit: Philippe Bourrinet, The Dutch and the German Communist Left (1900-68) (s.l. 2008)