Document everything with video, then call a lawyer and demand visitation rights which may get CPS involved.
Or, apply for custody. It’s an impossibility, of course, but gets the legal system involved. You will automatically lose, until you show them video.
Insist you would prefer she get help, but now she will be under observation. Which may moderate her behavior.
Unless your son wants to divorce her, which is a talk you should have, the best you can do is apply for parental (grandparent) rights.
GET EVERYTHING ON VIDEO FIRST, they can’t ignore video. Consider hiring a detective to help you gather evidence.
In MN, back in 2000....I did all that and it got me nowhere over 3 years. Its a HUGE uphill battle. The sick wife ignored judges orders multiple times for psych evaluations with no recourse for me except to file another motion and affidavit and drag her back into court ($1500 and 2 months wait/schedule time each iteration). She could stall and stall until the cows came home. Only after 18 months and 4 trips back to court did the judge crack down on her. ABSOLUTELY INFURIATING.
Perhaps different where you or the OP live, but the cost to the family will not be insignificant.
All in all, very well informed advice, though results may be very disappointing. Good job on advice, regardless. :)