Is it permissible to donate a sum of money that the deceased entrusted to the questioner, having advised her not to tell her brother about it, while the questioner knows that the brother would not donate it on behalf of the deceased?

You are not allowed to donate the money left by the deceased woman, as it is the right of the heirs and must be divided among them according to Islamic law. Therefore, you must hand it over to them, as it became their property immediately upon her death. It is stated in the Kuwaiti Fiqh Encyclopedia: "The heir acquires ownership of the deceased's inheritance by coercive ownership immediately upon the death of the deceased."