Coping with addiction/mental illness

My son and DIL recently went through a divorce. She has bipolar compounded by alcoholism and addictions to prescription and recreational drugs. He coped as best he could, but throughout their 6 year marriage she attempted suicide 5 times, is a cutter, and twice became wreckless with a gun to the point that authorities including a SWAT team became involved. My son is active duty AF, living on base. At one point she was banned from the base before the divorce and had to get an apartment of her own. 

For the safety of his child, who was home during most of the self harm events, my son divorced her. It seemed that she worsened significantly afterwards, and decided to cut off all communication with me. It saddens me, but I still send her texts and messages in hopes of someday maintaining communication. 

It has been about a year now and my son has custody, she gets limited visitation, but more often than not, calls to cancel because she is "sick." Several times she has come to the designated meeting points intoxicated, or accompanied by questionable "friends."  My son won't let my GS go in those instances.

My son tries and tries to get her to continue to go to her NA and AA meetings, counseling, but she and her family maintain that she doesn't have a problem, and that she is simply acting out because she is "heartbroken" and if they would just get back together everything would be fine.

Last week, her newest boyfriend totalled her car, was arrested for aggravated DUI, evading, fighting with the police and fleeing the scene of an accident. He was found with multiple prescription and illegal drugs, marijuana and open bottle of alcohol. DIL was not with him, but was at home, also intoxicated when the police went to notify her of the car wreck and so blitzed they called 9-1-1. 

My son has decided for the safety of his child, to get a restraining order against the BF. Herein lies my dilema... the in laws have been calling and calling and calling me telling me what a POS my son is, that he is only doing this to "get back at her", and that he needs to just leave her alone that she has found a new love and is finally happy. I asked if they knew what happened, if they were okay with it, and asked how differently they'd feel if she, or OUR GRANDCHILD was in the vehicle at the time.  They brush that off, saying well "they weren't, so it was just an accident..." 

I am torn between wanting to stay in communication for the sake of my grandson, and telling them to jump off the cliff!  Why don't they help her!?

I know she's sick. I get it. I have a sister who has the same issues, but I cannot and will not say it's okay to endanger our grandson and am 100% on my son's side about getting a restraining order.  

I guess what I am ultimately doing is venting, don't really have a question. This is a weekly burden and my grandson is only 8... We've got a long way to go and it's very, very, very hard..  

Thanks for reading this.