Well my guess is that he is not going to cross his mother. I suspect that he has had a lifetime of "putting up with her crap", meaning that he learned in childhood never to cross her or there would be consequences. Whether or not you yourself are willing to live with her continuing in her current behaviors towards you (and with the fact that your husband sees other women) is up to you.

Your children, though, seem to me to be a different manner. How old are they? It sounds like your husband is physically abusing them. You've asked him to stop, and he hasn't stopped. What does the therapist think of his methods of discipline? In addition, there are several family members who apparently routinely insult you and your kids, and you have a mother-in-law who "verbally attacks" you and your children. It was a struggle to get her to stop the abuse and leave your property. Your children, then, it sounds like, are being emotionally abused if not terrified. In addition, they are learning that it is okay to insult and their mother and ignore her wishes, family members do it all the time. They are also learning that, when they grow up, it is normal, accepted behavior to insult and mistreat women and children.

You have tried multiple reasonable ways to get your husband to change his behavior, and to get him to protect you and your children from family members. He apparently is unwilling and/or unable to do so. For the safety of your children, then, I agree with sophiesmom: it is time to leave.