Heck if I know. I wouldn't.Pray tell why would someone put an iMac on a coffee table?
I hate when people touch the screen.
Parenting by teaching limits & boundaries is very effective.
Are they his kids? i.e is he their parent?
My dad has his grandchildren over at times and he has his iMac on a coffee table.
Perhaps you fail to understand the meaning of "Grandparent"
Grandparents usually love their grandchildren & work together with their offspring in parenting their children.
But then again , in many cases they turn over their power to help and choose complacency.
All validated by excuses such as you've provided.