Hi,
I think, first and foremost, apply for Personal Protection Order. And I think your MIL has some other designs because if she really wanted all good, she would not have behaved the way she is behaving. And why on Earth does she want your baby? And how come your husband is ready for whatever nonsense his mother is saying? I think, the best for you is to leave him. I know it is a big step and you must be having inhibitions about how will you manage with two kids, but trust that you will anyway be better off with your kids minus your husband. Your husband is 21 and I think he is too immature to handle the responsibility of you. Because if it wasn't so, he would not have given each time to what is mother says. He doesn't have a developed mind to make up between right and wrong. And if he has the capability to understand that you are right, then all his senses go to drain when his mother tutor him. He comes in his mother's talks and he then loses the sense of right and wrong.
I think, if you will continue with him then the process of his feeling bad and saying sorry and then again hitting you and behaving irrationally will be an ongoing thing. You will have to live with his mother and his eccentricities. I do not think, you should do this to yourself and your kids as well. Your MIL has a wicked mind and that thought will affect your children too if you continue with this marriage. I suggest, be bold, be strong, have faith in yourself and the power above and set yourself away from this marriage and live a life of peace and dignity. There is no law that can separate a mother from the child, so do not give in to the harassment of your husband and MIL that they will take the kids away or you will have to. Seek help from government bodies and you will do good. Good Luck!
Belle Gan