Hello, it's good to talk with you again.
Children are very insightful. They may not know what their grandfather did is called abuse, but they knew that it was wrong and it hurt, especially if you had to protect them. They would also recognize that their parents did not treat them the same way.
The best way to approach the absence of the children's grandfather is to tell them the truth, just without the unnecessary details. For example, you can tell them that grandpa was not treating you nicely and you feel he did not treat them nicely either (use whatever words you feel describes the situation best). Tell them for that reason grandpa is not at home anymore. Emphasize that this was a choice you and grandpa decided was best for now. The closer to the truth you can be, the better. Kids are very good at knowing when someone is not telling the truth and so will accept a close to the truth explanation before an untruthful one.
It is also healthier for them to understand why their grandfather is not there. They know he was not nice to them and may also know he was not nice to you. Seeing that he is not there because of it shows them that there are consequences to behavior that hurts others. So though it is not an easy situation, it is healthy for the kids.
It sounds like your husband continues to create problems and does not see he is the cause or the center of the abuse. As we talked about before, as long as he refuses to see himself as part, if not all, of the problem, he is going to continue to be abusive. It is very healthy for you to move away from being with him until he can see he has problems that need addressed, if he is ever able to gain enough insight.
Let me know if I can help any further,