re: how do you feel?

Nope. Never.
Mom and dad are the decision makers in this family. Their grandparents merely carry out our wishes. I would never impose that burden on my parents. (being a disciplinarian)

I don't remember ever getting spanked by my grandparents. But nobody has permission to discipline our child like that... and I do mean nobody.

That's when I'd say, ok...I won't send them!! Absolutely not ok.