How should a husband deal with his parents who are trying to separate him from his wife by all means, and who mistreat the wife, saying things about her that are not true?

Allah Almighty has made the rights of parents obligatory and commanded to accompany them in this world with kindness, even if they strive to make one forsake His own right, glory be to Him. Part of their right is to support them, whether they are oppressors or oppressed. Supporting the oppressor is by preventing him and restraining him from injustice. Among the acts of filial piety is to restrain parents from oppressing the wife, especially if the oppression relates to her honor and dignity. The husband must ward off harm from his wife, and this is done by providing her with an independent dwelling, preventing the parents from entering upon her and being alone with her, and reminding them of the seriousness of assaulting a Muslim's honor.