Complex sentence: Because his mother was Jewish, Michael Wieck and his sister, Miriam (b.1925), were declared "Geltungsjuden" ("certified Jews"), and after Hitler came to power in 1933 they experienced the gradual ramping up of anti-Semitic discrimination and oppression.
Split into simpler sentences: Because his mother was Jewish, Wieck and his sister, Miriam (born 1925), were declared "Geltungsjuden" ("certified Jews"). After Adolf Hitler came to power in 1933 they experienced the gradual ramping up of anti-Semitic discrimination and oppression.