What is your advice to a father suffering from his disobedient teenage daughter who ran away from home and dated young men, and is it permissible for him to disown her, knowing that she insists on her actions and there are no signs of her repentance?

A girl is not permitted to run away from her father's house; it is forbidden (haram). If, in addition to that, she dates young men and spends nights with them, the sin is even greater. One should frequently supplicate for her guidance, and assign someone who influences her to advise her gently, and strive to get her married for the sake of chastity. The father should combine gentleness and firmness in dealing with her. As for disowning her: if the intent is to disown her actions, then it is required; but if it is to disown her lineage, then it is impermissible. If it means expelling her, then that will only increase the harm and corruption.