All Hell has broken loose in my family

My daughter and husband have been separated for about 6 months.  Yesterday, she found out he has been having an affair with a friend of hers, for the past 5 months.  My daughter went ballistic.  She put things on facebook about this other woman, included this woman's phone number for people to call her and tell her how proud they are that she destroyed my daughter's home.  My daughter also invited this woman to meet her face to face and called her names and what my daughter planned to do to her physically.
She called this woman names that I will not repeat and now, my wife and her husband's folks are involved.  The Police have been notified and now my wife is meeting with them. etc. as I write this.
I hate this because they have 3 children, 14, 12 and 8.  The kids will not talk to their dad because of what he has done and I am sure my daughter has caused some of their feelings.  She is crazy, like I used to be when I was her age.  My daughter-in-law, who is a nurse is down there now, trying to calm her down and talk some sense to her.  My daughter hasn't slept since she found this out and if she is not careful, she is going to crash and burn.  She has already changed her name back to her maiden name on Facebook and things are a real mess.
They do not want to get me too heavily involved in this.  I have always liked my son-in-law but, if he does something physical to my daughter, then he will answer to me and I don't think he is ready for that.
For those of you who bother to read this, keep my family in your prayers.  This is such a tragic and sad mess.