What should I do about involuntarily consuming food and drink derived from usurious money? Should I cut ties with my father and leave home, knowing that my father lives off usurious profits from money he inherited from my grandfather, and he cannot invest it in trade for fear of losing it? I am a student unable to work, and my mother is ill and unable to work, and I have tried advising them both without success?

Your father can invest the money in Islamic banks to avoid riba (usury), which holds no blessings. He should be advised with wisdom and good counsel. As for dealing with his money, if it is mixed (lawful and unlawful), it is permissible. However, if it is entirely unlawful, it is not permissible to deal with it except out of dire necessity, like the need of a poor person, in which case he may take from it according to his need, and it becomes lawful for him. But if the son is self-sufficient with lawful money, then it is forbidden for him to deal with his father regarding the actual unlawful money itself.