Is it permissible to give the debt of a deceased woman who has no heirs to the questioner's poor sister and mother?

The heirs must repay their father's debt from his estate. If it is impossible to identify the heirs of the female creditor, and one despairs of doing so, the money should be given as charity on her behalf, with a guarantee that if an heir appears in the future, the debt will be paid. Money whose owner is unknown should be spent on the welfare of Muslims. If the mother and sister are poor, it is permissible to give the charity to them.