Is it permissible to marry a girl of good religion and character whose father has been sentenced to death, despite the father's objection to that out of fear of security repercussions, and after many attempts to convince him?

Obedience to parents takes precedence over marriage to a specific girl, unless the son fears harm to himself by not marrying her. Allah may turn your heart away from her, and you may find someone better if you leave her out of dutifulness to your father.