Is it permissible to give zakat on behalf of a deceased father who did not pay zakat on his wealth, and should it be given from his wealth or from the son's private wealth, and is it permissible to give it to an unemployed brother?

If a person dies and has an obligatory Zakat debt, his heirs must pay it from his estate before its distribution, because it is considered a debt upon him. It is estimated through ijtihad (independent reasoning) and dominant assumption for the past years, so 2.5% of the money is paid, with the Zakat of each year being deducted from the subsequent amount.

It is permissible for one of the heirs or others to donate and pay the Zakat from their own money instead of from the deceased's estate.

As for paying Zakat to a brother, it is not permissible to pay it to someone whom one is obligated to support. However, if the father has passed away and support is no longer obligatory, and the brother's share of the inheritance is insufficient and renders him poor, then it is permissible to give him from the Zakat, provided that his share is not enough to sustain himself and his family for a year.