LW1: You describe your DIL as "the mother of our only grandchildren" but there's more to her than that. She also has a career, hobbies, interests, etc. You don't mention what kind of relationship you had before the children, so I wonder how much interest you showed in her before them. 

You also mentioned that they stay home for holidays. I don't have children, but among my friends who do, I've seen a return to holidays at home. As families are larger/blended, it is stressful to pack the kids up and make the rounds.