What is the ruling regarding a husband telling his mother: "You are my wife and you will do everything I tell you," and to what extent is his wife's warning to him about that appropriate?

Your husband's playful remark to his mother, "You are my wife," does not affect the marital bond, nor does it constitute a divorce or ẓihār. However, he should not utter such a phrase, even in jest, because it is objectionable. The Lawgiver has forbidden taking the verses of Allah in jest and has prohibited making light of them.