It is more likely that Rudolf was actually a grandchild, rather than child, of Emil Joseph (11.01.1864 in Filehne) and Hulda Joseph-Jacobsohn (01.04.1876 in Lauenburg), judging from their ages, though they are listed as his parents on his Amsterdam Card.
Rudolf emigrated to Amsterdam on 10.04.1937.
Emil and Hulda lived at Detmolder Str. 55 in Berlin-Wilmersdorf, and were deported from Berlin to the Theresienstadt Ghetto on 25.08.1942, where Emil died on 14.02.1943 and his wife perished on an unknown date. (Bundesarchiv Gedenkbuch, Gedenkbuch Berlins, Amsterdam City Card)