Complex sentence: A source of considerable annoyance for him was that three of his sisters married Jewish men, and in 1946, he claimed under interrogation that this ruined his reputation in the army, forcing him to leave the Reichswehr.
Split into simpler sentences: A source of considerable annoyance for him was the fact that three of his sisters had married Jewish men. In 1946, he claimed under interrogation that this had ruined his reputation in the army, forcing him to leave the Reichswehr.