What else can you tell us about the historicity Jesus? And how is it you are able to say anything about this person that is purported to have lived 2000 years ago?
Approximately a third of the people on earth belong to some sort of Christian religion. The virginity of Mary, the mother of Jesus, at least at the time of His conception, is a Very Big Deal to all of them, as are the stories around His birth.
The prospect of the tradition(s)' having missed something as blatantly obvious as the birth of a second son at the exact same time is ridiculous.
