Is it permissible for a brother to pay the expiations of his brother who is unable to fast and perform expiations, from the zakat of his own money, so that it becomes an expiation for the incapacitated and zakat for the brother at the same time, knowing that the incapacitated is not eligible for zakat and is not negligent in the matter of expiations?

It is not permissible to give zakat to pay off the debt of expiations (kaffarat), whether the debt is owed by the giver of zakat himself or by another person. As for the giver of zakat, it is because expiation and zakat are two independent obligations that must be fulfilled with two different types of wealth. As for another person, zakat is not given to someone merely because they owe an expiation debt. However, if they are indebted and in need (poor or indigent), then the zakat giver may give them zakat, and then that person may dispose of it by paying off the expiation debt or for other needs.