Sort of similar situation. My mum died after a long illness. Prior to her death, my married sister, her hubby and the kids would come over every Saturday, though to be honest I couldn't see why as all they did was let my mum wait on them hand and foot, ill though she was. Still I suppose she was glad they came...
Anyway, after she died, I saw my sister and her family just twice within the few weeks after, and there was a long period when they didn't call or anything. I tried to make an effort one Christmas, got them all prezzies and everything, but it was a dead loss. I gave up in the end - I no longer have a sister, and haven't now for just over ten years. I miss not having family now, but no way do I miss them.