So sorry you're in this situation, betty. IMO, you have gotten a lot of good advice here regarding IF your ILs try to reconnect. Also, I understand your worry about their going NC again and, this time, hurting your DDs. However, I think you've come up w/ the solution to that, by saying you would keep the kids out of it at first. I would add I would keep the contact low for a long time.
I think it's interesting that your ILs have also CO their own parents (both sets? his and hers?). And that you and DH are still friendly w/ those parents/his GPs/your DDs' GGPs. Is it possible they see your continued relationship w/ their parents as a kind of betrayal? I'm sure these relationships were not maintained for that reason, but perhaps that's how your ILs see it? If that's so, and they are still NC w/ their parents, then I doubt they will truly reach out to you any time soon.
Or maybe DH tried to intercede on the part of his GPs? If he had/has a really good relationship w/ them, it's not surprising. But if he did, perhaps that's why his parents are angry at him (and you, by extension)? Again, if so, chances are they won't be extending any olive branches in the near future.
Then again, perhaps they are just odd people who get offended by everyone. In that case, I realize it's harder to know what they might do. It doesn't sound as if they are going to try to reconcile, but I agree it's good to be prepared.
Besides, I think this season tends to make us all think back on family history, etc., good or bad. Now that you have some ideas of how to handle a possible attempt at resuming contact, please try to relax and enjoy this colorful season.