God bless you. I would encourage you to do this only as a last resort and here is why. Your poor husband has already had the main woman in his life (his mom) manipulate and control him. What he needs now is a wife that trusts him and builds him up, not one that takes over. I know your heart is in the right place and you want to protect your husband and child from this toxic woman, but please do all you can to build up your husband so he can do what he needs to do.
Do you talk about your mother-in-law a lot? If you are like I was and you do, I would encourage you not to unless you have to and then keep it very short. I speak from experience. I could write a book several inches thick about the lies and manipulations of my mother-in-law. However I don’t think I helped the situation because after encounter with her, after every visit, phone call or birthday card my poor husband would get a huge earful from me! I would sit and analyze everything with the man until he was worn thin. I thought I was actually helping if you can believe that but in reality I was tearing him apart. He would “get it” emotionally from his mom and then “get it” from me it was like a one-two-punch in boxing.
With God’s grace I was able to back away a little bit and let God in more. We both still knew his mother was abusive and a bit crazy but we didn’t have to talk about it all the time. When I knew my husband was going to call her I gave him a hug and said “I know it’s going to be hard I will be praying for you.” and that was it! It was wonderful. When I knew he had a decision to make about visiting her with the family I told him “I trust you, you are the man of the house I know you will do what is best for us and to protect our children.” and I told him I was praying for him it was beautiful!
This doesn’t mean everything was or is perfect for us and it won’t be for you either. However I want to encourage you to do all you can to build up your husband. Tell him you believe in him, tell him you are happy you married him and you trust him to be a good husband and father. He might not feel you have confidence in him because of past mistakes he has made so it might be good to try and tell him you trust him. Trust is so important in a healthy marriage. God bless you and please be assured of my prayers.