So,whats the big issue about Mary and Joseph having sex like any normal married couple and being blessed with children as a result?
But has to do with the fact that the Bible does not say that the ones called brothers and sisters are Marys children.
They may or may not be but personally I do not believe they were and I have gave the reasons.
This is Jesus speaking in the Psalms...
Psa 69:8 I am become a stranger unto my brethren, and an alien unto my mother's children.
This is part of the prayer that Jesus was praying to God just before the Crucifixion...