What is the ruling on benefiting from land that the grandfather acquired by deceiving its owner, then the owner forgave him before his death, and the land remained registered in the name of the grandfather's heirs?

Usurping land is a grave sin. The usurper, or whoever subsequently acquires the usurped land, must return it to its owner or their heirs. If the owner of the land forgives the usurper during their death illness, this does not nullify the right of their heirs to the land. This is because forgiveness often constitutes absolution from sin only, and not from the obligation to restore the right. Even if the forgiveness was intended to absolve both matters, the actions of a sick person during their death illness, such as gifting or absolving debts, are treated as a will. Therefore, such actions are only effective within the limits of one-third of their property, and anything exceeding that is dependent on the approval of the heirs.