Your mother in law is having sex with your daughter's husband. How do you handle the situation? This video will give you some advice that may help you deal with your mother-in-law. This video focuses on the first step: taking the lead in the conversation. Tell her that she is hurting your marriage and is not welcome in your home. Your mother-in-law will likely react in anger and try to make you feel guilty. Creating boundaries creates power in love, so do not give into her temptation..