Pray to Allah to guide him. Introduce him to some people of knowledge. He may recognize his bad deed. You should be a good example for him. If you engage yourself in the good deeds of praying, fasting and reciting of the Qur’ân, he may feel the good atmosphere of your house as he has never known it before.

If you really fear that he may approach your household, then beware of leaving him alone with them in the house. If, however, you fear that his presence is a trial that is too difficult for your family to bear, you can provide your father with seperate accomodations and not allow him to reside in the same home with your family. 

Keep in mind, though, that a father deserves good treatment from his son even if he is bad. Ibn `Abbas related: “Any Muslim who has Muslim parents and he treats them good every day, Allah will open for him two doors to Paradise, one door for each parent. If he upsets one of them, Allah will not be pleased with him until the parent is pleased with him.” 

Someone asked: "What if they oppress him?" 

He said: “Even if they oppress him.” [Related by al-Bukhârî in al-Adab al-Mufrid]