How can the money from usurious loans belonging to a deceased brother be purified, and what is the legitimate percentage that must be given out? Is it permissible to give this money to another brother for marriage?

If a brother borrowed from banks and is paying interest, there is no usurious interest in his money because he is the giver, not the taker. However, if he has money deposited in banks and usurious interest accrued on it, then it is not permissible for him or his heirs to take this interest; they are only entitled to the principal. This interest should be spent on general Muslim welfare, such as orphanages and hospitals, or given to the poor. It is permissible to give it to the brother if he is poor.