What is the ruling regarding a father who orders his children to deal in usury, then troubles and deprives of his wealth those children who refuse to do so, then demands from them the lawful money they have earned, seizes their building materials to use for his own construction, and abandons and invokes curses upon any of his children who object?

It is not permissible to obey a father if he commands dealing with usury, because obedience is only in what is good. Nor is it permissible for him to demand money from his children or take it from them as long as he is not in need. The children must be patient and gentle with him, and respond to his ill-treatment with kindness, as Allah Almighty says: "Repel [evil] with that which is better, and suddenly he to whom there was enmity between you and him will become as though he was a devoted friend." This is due to the great right the father has. There is no harm in using ambiguous statements or even lying to the father to conceal money that he does not need. It is also possible to seek help from people of goodness and righteousness to reconcile between the two parties.