Is it permissible to pay off the debt of the deceased husband's father to the husband's poor brother with the intention of settling the debt and having it be a charity on behalf of the deceased owner of the money, in the event that the heirs of the owner of the money are unknown?

The heirs of the owner of the money must be sought by all means and the amount delivered to them. If that is not possible, then the amount should be given as charity with the intention that its reward be for him, in any charitable cause, while considering the needs of Muslims. It is advised not to give it to a brother to avoid favoritism and accusations.