Is the remaining portion of the usufructuary lease amount for the mother's residence after her death considered part of the inheritance or a right of the son?

The true nature of the amount the mother gave her son to complete the house payment must be determined. If it was a donation or a gift, then the amount belongs to the son, and the mother's presence in the house is a reward for her kindness. However, if the amount was a loan, it remains a debt owed by the son, and if the mother dies before it is repaid, it becomes part of her estate. If the son and mother agreed that the debt would be repaid by the mother's stay in the house, then the duration and its equivalent rent should be calculated and deducted from the debt, and whatever remains after her death becomes part of her estate.