Is it obligatory to return the money that the father took from his wife to buy land and build a house on it, and the unpaid deferred dowry? And does the son's repayment of these debts make him the owner of the land, or does its ownership revert to the deceased father and get divided among the heirs? And is it permissible to disburse these amounts from the son's Zakat money before its due time to absolve the father's liability?

If the mother absolves her husband of a debt, the debt does not return after the absolution. None of the heirs has the right to pay this debt from the inheritance except with the consent of all adult, mature heirs. The deferred dowry (mu'akhkhar sadaq) is considered a debt owed by the husband, becoming due upon death or divorce. It is not permissible to pay the debt of the deceased from zakat (definition) according to the majority of jurists, because the debtor (gharim (definition)) is the deceased and cannot be paid, and because the Prophet, peace and blessings be upon him, did not pay the debts of the deceased from zakat.