Jeezo pete - What a story.
To answer your last question the only time a Dr, Medical professional or Clergy are mandated to report are when they with their clinical knowledge and skills feel that an individual is a danger to themselves or others.
Now who knows what really happened, it certainly sounds like this group of folks is not the cream of society, with prior references to police, and concerns about having "medical Marijuana" around 5 kids.
However if they NW reported it to the hospital that her daughter attempted to harm herself in anyway the hospital would be mandated to report that to Children services. But if they decided that they would tell a different story, and everyone told the same story at the hospital, then no report would have been made. There is no way to MAKE someone tell the truth.
I would however consider talking with your Attorney in regard to your parenting agreement given what is going on in that home. I know I would not want my young child in a home where marijuana is being used (and I am not a prude but I wouldn't want my kid being exposed to it) there are other kids there, that aren't siblings with emotional issues, esp teenage boys. Just seems like a perfect storm for something unfavorable to happen.
I will send up a prayer, and mojo your way for a peaceful week, and that your DD isn't too involved or effected by any of this.