An Australian teenager is believed to have died in a Syrian jail after being held for three years, his family said Monday as they pleaded for the return of other detained women and children. Yusuf Zahab, 17, died from “uncertain causes” in northeast Syria at the Al-Sinaa prison, Human Rights Watch said. Kurdish-led forces have held Islamic State suspects at the prison, which was the site of intense fighting between IS fighters and US-backed troops earlier this year. An Australian teenager, wrongfully detained in northeast Syria after being forced as a child to live under the Islamic State (ISI…