Hello and thank you for your question.
What an awful situation to have to witness... especially for the young children who are being affected no doubt by all of this fighting and anger. Can you tell me how long this has been going on? Also do you live nearby the children?
Okay, thank you for the additional information. Your daughter is fortunate in that she has many options available to her (through your offers), and maybe in time she will opt for one of these choices.
It's really good that you are taking the kids as often as possible and allowing them to get away from the chaos. When you say that she returns to the home, is that where her husband is? Or is he somewhere else? If they are still in the same house then one of them (typically the husband) needs to move out. Your daughter should talk to her attorney about this.
Right now, your daughter and son-in-law are going through the toughest time of a divorce, and once it's closer to being done or is done, things typically do settle down...
In the meantime, be sure to keep an open line of communication with the kids so they feel they can talk with you about anything. You could suggest to your daughter that these behaviors are stressing out the kids and that she needs to think of them first and stop acting out for their sake.
You could suggest to her that she gets some counseling for the kids and for her, to help them all through this situation. That you are upset about what this is doing to the kids, and only have their best interest at heart. That is really all you can do, unless there is violence in the home or you worry about someone getting harmed then you could report to the police.
You really need to take care of yourself as well. If you give me your zip code I could find some therapists in your area that maybe your daughter could contact about her and the kids.