Will a brother be sinful if he refuses to care for his sick wife despite the availability of assistance, and is it permissible for the family to ask their adopted daughter to care for her mother?

The husband must provide for his wife according to what is customary and not abandon her, and he must provide a servant for her if she is ill and unable to serve herself. As for the woman he sponsors, she is not obligated to serve the sick wife, and the wife is not permitted to disobey her husband for the sake of this care. Furthermore, it is not permissible to seek to divorce the wife, as this is clear injustice and a great sin.