Is a son's disobedience to his father's command not to lead the worshippers in Tarawih prayer, out of fear for him of imprisonment, considered an act of disobedience (ʿuquq) or a sin, and what should he do?

Obeying one's parents is obligatory unless it involves disobedience [to Allah]. And since the father commanded to leave the imamate out of fear of the oppressors, while an alternative exists, obeying him becomes obligatory, because leading Tarawih prayer is not obligatory, while obeying one's father is obligatory.