What is the ruling on a man marrying a woman without the knowledge of her family, except for her young brother, and is a young brother considered a guardian (wali) when there are two older brothers and parents who are unaware?

If the father and brothers prevent a woman from marrying a man whose religious commitment and character are pleasing, without a valid Shari'ah excuse, their guardianship falls away and transfers to the next in line among the guardians. If the younger brother is a Muslim, mature, and sane, his guardianship is valid, and the marriage is valid if its conditions are met. This is the view of the Hanbalis and the prevailing opinion among the Hanafis. However, if the father and brothers prevent her for a valid Shari'ah excuse, or if they do not prevent her from marrying a righteous man, then the marriage is invalid if the distant guardian undertakes the contract while a closer guardian exists and is not preventing her or is not absent.