You didn't say what happened to the mother. If you proceed in court, you would need to give notice to both the father and the mother with a non parental petition for custody. If the mother is no longer living and the father would consent to you having custody, then it shouldn't be a problem. It may even be simpler for the father to sign a power of attorney for this purpose. If you proceed in court, the court will do a background check of you that includes looking at your criminal background.
