I remember Michael saying that one of his sister's final wishes was for him to get along with Nancy and he said he would for her. So I am not sure why it is that Michael always seems a bit removed from the family in these last few days or who may be responsible.
Maybe Nancy has just been so defeated by ten years of this that she can't think of anything but Ronnie right now. Michael is a little intense, but I can't imagine Nancy not caring for someone who loved his Dad/Ronnie so much. Ron and Patti seem to just be letting Nancy drift along on her own ( unless she's got an escort ) there in Washington - Michael should just go and be by her side whenever she's alone - stand by her chair/ guide her where she needs to go. He shouldn't care what the others say, he should just do it.