{{{{{{{{{{Parker}}}}}}}}}}}}}} I know what you're going through. Been there, done that! In fact, I'm going through pretty much the same thing you are right now.
Most States DO NOT have GPVR, period. The laws of your state at least give you the option of Custody. You BET I would file for Custody in nothing flat... if you think you can manage all the crap that's gonna come down the pike.
Before you even begin, your motto should always be IN THE BEST INTEREST OF THE CHILD. (BTW, I was active in GPVR rights some years back.)
Your son, as well as mine, are GUILTY by association. What is more important; not wanting to hurt someone's feelings OR allowing their child(ren) to be hurt by their mother and their living conditions?? Give me a break!!
Get a restraining order on that broad! It may not keep her away from your front door, but once that RO is filed, if she voilates it, it will no longer be a minor thing! Some states carry different penalties for violating an RO.
If you have any more questions, I'll be more than glad to try and answer them. The only problem is that every State has different laws and statutes.
The fact that your grandchild's mother is so abusive will really work in your favor. You'd be surprised to know how many grandparents are raising their grandkids. There's support and support groups for these people.
My best to you, Parker!
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Psalm 119:105 Thy word is a lamp unto my feet, and a light unto my path.