Fahn and his first wife had two daughters. His wife died when he was 25 years old. Fahn's eldest daughter Hana was later murdered in the Holocaust while her two daughters survived. In 1905, Fahn remarried to a woman from the city of Bolechow, with whom he had a son and a daughter. Yafa, Fahn's daughter from his second marriage, died at age nine while Fahn and his family were living in Vienna. Yosef, the sickly son from Fahn's second marriage, eventually had a son of his own but he and his entire family were murdered during the Holocaust.