How can one confirm that the father is afflicted with magic (sihr), and what is the method for his treatment?

It cannot be definitively asserted that a person is bewitched, possessed by a jinn, or afflicted by envy unless strong indications are present; otherwise, the default assumption is that whatever one complains of has organic causes that necessitate consulting physicians. The cure for sorcery, whether it exists or not, is lawful Ruqyah (exorcism) using the Qur’an and Sunnah, and turning to Allah Almighty, while warning against resorting to charlatans and sorcerers.