What a terribly difficult situation. So many have already been through it and more always follow. Sorry you and your family are now dealing with it. It's not an easy or simple issue to "fix". I really hope that your daughter has the foresight and strength to get through this, and she'll need all the caring and compassionate (but strict and no nonsense) support that she can get from you and the rest of the family and friends.
Please don't make the mistake that many make in believing that her abusive husband will let this go. And don't try to "protect her kids" from the reality of what their "daddy" has been doing all these years. They need to be made painfully aware of what a scumbag he is in order to "break the cycle". Please explain to your daughter that as long as she protects them (her kids) from the reality that is "dad", she is setting them up, and their future children, to go through exactly the same thing! It's what they think is normal and accepted and your daughter is reinforcing that belief.
I wish all of you the best, and a clean break from the mess.