The issue with her folks it a tough one. You know how you feel about your kids, why would you expect them to feel differently about their kid? I mean right, wrong or otherwise, when it comes to your kids you are still going to love them and support them. Why would you expect any less from her folks?
I'm not saying that what they are doing is right, just trying to give you a little different view of things so that maybe you can let some of the anger go.
"Our life is what our thoughts make it."
Marcus Aurelius