is it permissible for the brothers or the sons of a man or a woman to be witnesses to their marriage contract, given that the Waliy (a legally accountable person acting for a woman regarding marriage) of the woman is her father or one of her brothers?
It is permissible for a man to be a witness to his brother's marriage contract. However, it is impermissible for a son to be a witness to his father's marriage contract, or a father to be a witness to his son's marriage contract. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.