Why is this a surprise? My father was estranged from ALL of his relatives for many years during his second marriage. Since that marriage ended, he has re-established contact with his family, although his relations with many individuals remain somewhat strained. He married Vanda, his third wife, nearly 4 years ago, and this will be the first big family event that they attend together. According to my father, the deciding factor behind his not attending family events has been his wife's reluctance to meet so many people all at once, particularly in the face of her being his third wife and being a Brazilian national who has been in the US for only 6 years and who still does not speak English very well; as she puts it, she does not want to "look small" in front of his family.
According to my father, on this occasion Vanda agreed to accompany him to tomorrow's dinner provided one condition was met: that I also would be at the dinner. I don't know what else may have shifted for Vanda; I could speculate, of course, but until I hear what she has to say, nothing I might come up with has any basis in reality. Perhaps she feels more secure now than before; after all, she has been a US permanent resident long enough that she has been able to file her application for US citizenship.
Tomorrow will be an interesting day.