This family does sound somewhat disfunctional.........Mother visits for two weeks, DIL disappears and won't communicate and son hides in his work.
Perhaps it's time to have a conversation with son and DIL to get to the bottom of the problem, there could be problems within their marriage, who knows.
The fact that you want to have contact with your grandchildren is the important thing for you so only you can start that conversation if the adults are so distracted and distant.
In light of our current weather.......
Water Pollution -“ A National Disgrace”? A case for renationalisation?
BBC Two- Surgeons: At the edge of Life