I've heard the issue come up numerous times and here's my "out of the box" idea.  When the grandparents want to come from out of town and stay longer than 5 days, I suggest the parents give them a schedule for the kids' schools and activities, then hand them the keys to the car.  Meanwhile, the parents go to a hotel down the street! They should stay in town so they can work etc., but let the grandparents watch the kids alone in the kids' own environment. 

I would have loved that when my kids were little. Unfortunately I had the opposite problem. The older generations in my family rarely visited and never for more than 3 days. 

Cindy