I think that if you try and show them some compassion and let them see their dead daughters only child you wont regret it. Some of the posts here are very OTT. They are not going to run off to Mexico with the child.
As a grandparent myself I am able to see things from both sides, while many here cant.
You have no idea what the GP will and will not do. You don’t even know them.
What we do know is what the OP has told us. Two times the GP threatened to take his son away from him via legal action. That is a real threat that he needs to take seriously. They have already promised him that they intend to take custody of his son. Why are you continually ignoring this?
I'd love to watch your reaction if someone threatened to take legal action to take your children away from you.
And you are wrong that other posters here cannot see things from all sides. The thing is that others here have experiences that YOU DO NOT have.
For example, I have a nephew who lost all rights to even have visits with his son because his ex-wife’s mother decided that she wanted 100% custody and she got it. He took the stance that you are suggesting, be kind, don’t distrust them, blah blah. She and her husband were able to get custody because they are filthy rich, they are close friends with all the judges, and my nephew had a few things in his past. (Like 2 DWI’s 15 years prior while in the military… in VA Beach for riding a bike back to the hotel. Yep a DWI while riding a bike. And he lost his son over that.) Oh, and to make matters worse, the Grandmother who got 100% custody of his son, is a raging alcoholic. But she knew all the judges, many of whom are her drinking buddies.
You clearly have no idea the depth of horror that some grandparents will do to get control of their grandchildren.
My nephew has not seen his son in 10 years. He does have another son with his first wife. They get along great and are very good co-parents. He is an excellent father.