You would have to bring a legal action in chancery court in which you will prove, by medical evidence and testimony, that your father is incompetent, so that the court will declare him legally incompetent and appoint a guardian; you will also ask that the guardian be you and have to prove that his wife (who would normally get that role) is not capable of it. This could be a difficult, expensive suit, if the wife opposes it; you should consult with an elder law attorney in detail to better understand what is involved and what needs to be done.