What is to be said to a father who is unjust between his two wives, spending many times more on one than the other, and refuses religious advice?

Sufficient to deter injustice between wives is the Prophet's (peace be upon him) saying: "Whoever has two wives and inclines to one of them more than the other, will come on the Day of Resurrection with one of his sides fallen." We ask Allah to guide your father to justice and keep him away from injustice.