Having read only some of the posts, this may have been already said.
Yes, your sons on/off girlfriend has every right to be angry with your son, but no one should use their children as 'weapons', to hurt someone else, because ultimately, it is the children that suffer.
You might need to have a chat with the girlfriend and explain that you only want to have a relationship with your newly discovered grandchild, but not with his mother, as you consider her as your sons partner. That might appease her, as she may be scared of losing you too, even though she is going the wrong way about it.
I live in a small fishing village where everyone basically knows everyone else. Both my daughters have failed first marriages and there are half siblings and step siblings now they are with new partners, but, we all rub along nicely for the sake of the children and they are all happy and confident children knowing that.
It's so sad when folk start saying you have to choose this child over that child, but hope you can get it sorted without going to court. All that does is make the lawyers rich.
Alphabetical girls and boys names January 2024