Is it permissible to work on agricultural land that the father seized from his father by force, knowing that he has siblings who have not taken their share and have not claimed it for fear of discord and severing kinship ties?

It is not permissible for a Muslim to work on usurped land, because it is an affirmation of the usurper's wrongdoing, an aid to his sin, and a cooperation with him in sin and transgression. Allah Almighty says: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression."