I'm sorry you are in such distress. My son just went through a long, ugly custody battle, but he prevailed. I learned a few tricks while it was going on and, since I've been in therapy forever, I already knew them...it was sometimes hard to apply them, but they helped me and still help me.
1/ It is useless to worry. You have no control over the outcome of this case and worrying and becoming a nervous wreck won't change that.
2/You can only control yourself...not your daughter, her Integrated Listening Systems (ILS), or her ex. That means that unless you want to go for custody yourself or take them to court to try for visitation (not sure why you didn't already try to get custody...that's not part of your s hared story) you are really not going to affect what happens. And worrying and getting sick over it won't help. Only action will change things.
So, if you are really worried about your grands, in my opinion best to put your worry into action and go to court for visitation rights or for shared custody.
I have no idea what the outcome will be, but hopefully your grand's parents will be shocked into getting help so they can get custody back.
But all of this is not within your control. It's painful, heartbreaking and terribly upsetting, but it helps to keep things in perspective. Today, at court, you can not change the outcome.
Later, if you choose, you can always have your day in court. THAT you can control, what YOU do.
I don't know if this helped, but I hope so. I'm sorry again that you are in such a hurtful situation, but try to mentally let go of the outcome. If you are religious, put it in God's hands.