How can one deal with a father who wrongs his son, favors him over his siblings, lies about him, slanders him, accuses him of disobedience, does not understand his health conditions, and even rejoices in his illness?

If you are unable to earn a living, and your father is affluent, then he must spend on you equitably and provide you with medicine without reproach or harm. He must also be just among his children. You, in turn, must be dutiful and kind to your father, for his wrongdoing towards you does not negate his right to filial piety. It is not permissible for you to address him disrespectfully or to be disobedient. Rather, you must address him with gentleness and reverence, as Allah Almighty says: "So do not say to them [anything that indicates] disapproval and do not scold them but speak to them a noble statement. And lower to them the wing of humility out of mercy and say, 'My Lord, have mercy upon them as they brought me up [when I was] small.'"