Michael said in his book he did live with his father and Nancy for a while when Patti and Ron were small. I think he was older, close to the teen years. It didn't go well as they didn't have a bedroom for him and he felt left out of everything. Things have gone much better in their relationship since he is married and has children. Michael talked about it in his book in more detail. I think it would be a mistake to say he is distant from them. If I were going to a funeral I would be with my husband and children and no one else. From the book, he said they had worked out their misunderstandings. He had a difficult time living a normal life and making a living when his dad was president. A lot of children of presidents have problems like that. You get lots of criticism no matter what you do.
Well, I did go to a funeral in April, my Dad's. I went with my wife and daughters, but I was there for my mother, and my family was there for me. All I was saying is that their relationship, while close and cordial, is not a mother son relationship. That makes this situation somewhat awkward. Many, many people will have that kind of awkward situation in the future, given the divorce rate these days.
For example, my sister in law is married to her third husband. If she should die before he does, 3 of the 5 of her kids will be in the same situation, it will be their mother's funeral, but her husband will not be their father. (They all get along with him fabulously, and pretty much have from day one of the marriage, so it would be somewhat less awkward than the situation with Michael and Nancy).