How can stolen money be returned from the grandfather after his death and the distribution of the inheritance, and is it sufficient to give it as charity on his behalf?

Theft is one of the major sins. The thief must repent to Allah and return what he stole to its owner or to his heirs if the owner has died. It is not sufficient to give the stolen money away in charity, because ownership transfers to the heirs. If it is impossible to return the money because its owner is unknown, then it should be given in charity for public welfare or to the poor. There is no need to inform the heirs that the thief is the culprit; it is sufficient to deliver their right to them, clarifying that the money belonged to their ancestor.