Is it permissible to help a brother repay his usurious loans to alleviate the distress of the guarantor (the maternal uncle) who paid the amounts on his behalf?

It is not permissible to repay the excess amount of usurious debts unless the person is compelled to do so. It is permissible to help a brother repay a usurious debt if he has repented and is compelled to pay it, and it is more appropriate if the assistance is only for the principal amount. However, if he has not repented from usury, it is not permissible to help him. The person who guaranteed your brother in a usurious transaction is also sinful, and both of them must be advised about the seriousness of usury, the prohibition of dealing with it, and the necessity of repenting from it.