Parents are busy and so are their kids which is why grandparents should be sensitive to the overscheduled world that they live in. How do they do that? They don't demand or expect visits to occur at their convenience. Instead go with the flow. Once a week would be ideal but not necessarily a reality. So when grandparents push by calling and texting
about visits, the parents interpret it as pushiness and may push back by calling a time out.
If this happens then comply and don't bug them about it. Learn from it.