How can one deal with a harsh and stern father who does not care for his grandchildren, whose wife expels them in his absence, despite attempts to gain his approval, and the feelings of tension when visiting him?

It is permissible for a Muslim to perform ruqyah on himself, whether afflicted or not. A child must be keen to please and honor his father in a way that does not harm himself. It would be preferable if he always invited his father to his home and honored him. If an opportunity arises to visit the father's house, he should do so, and he should maintain the dhikr (remembrances of Allah) that are authentically reported. If sitting at home becomes difficult, he should coordinate with him a visit to a relative or a scholar, or take him out for a stroll outside the city.