What is the ruling on a wife refusing to care for her mother-in-law, who causes problems and demands that the wife pay for her mother-in-law's accommodation in a hotel, especially since the care of the mother-in-law would be shared equally between the wife and the husband's sister?

Your wife's brother has no right to dictate how long your mother stays in your home, or to impose the cost of her mother's accommodation in a hotel. Children must care for and spend on their mother if she is in need. A maid can be hired for this purpose. There is no necessary connection between your mother staying in your home and caring for your wife's mother.