I have always believed that a married man’s FIRST loyalty is to his wife. But not when she is being deliberately petty and/or hurtful to his family, and is digging in her heels on the subject. Then he has call her out about her behavior. Likewise, a son who sees his wife being hurt by his family for no just cause, should stand up for her and insist that she be treated with respect.
It can happen that someone marries someone of whom the parents truly disapprove (he or she comes from a family of a different socio-economic, religious, or intellectual background, they are disappointed in the person’s choice of profession or lack thereof, etc.), but that does not give anyone the right to act with disrespect towards that in-law child. You cannot force someone to love you, but you can expect them to treat you with derech eretz.