What is the ruling on benefiting from agricultural land inherited by sons from their fathers, knowing that their sixth grandfather usurped it from a man he killed, and is it permissible for them to give charity from its proceeds when they have no other source of livelihood?

Allah has forbidden usurpation (Ghasb) due to its nature of transgressing against the property of others. The usurper, and anyone who has acquired usurped property by any means, must return it to its owner or their heirs and actively seek them out. If they cannot find them, then it is obligatory to dispose of it by spending it on charitable causes. It is not permissible to spend from it on oneself or on those whose maintenance is obligatory upon him. Furthermore, he must pay the value of the benefits of the land that he rendered unproductive.