I have largely avoided the Religion Forum for years and I will not be debating the Catholic v. Protestant beliefs on this subject.
However, I would like to point out one thing for consideration:
There was NOTHING "normal" about Mary and Joseph's marriage. The Holy Family WAS NOT a "normal" family, they the most decidedly abnormal family imaginable. When God sends angels to inform you that your Child will be the Son of God, EVERY pretense of normalcy is pushed aside. All good parents realize their responsibilities to their children's well-being, but no parents have ever had this responsibility on the level of Mary and Joseph. I cannot begin to fathom how incredible it was to be tasked with this, but I would imagine that any presuppositions about what a marriage should be like would be pushed aside because when what could possibly be more important than actually raising God Incarnate?
Since the Lord commands us to be fruitful and multiply, it is not unreasonable to conclude that Mary and Joseph did just that.
I first learned that Jesus had brothers and sisters in a bible study class taught at a Catholic church by a Catholic priest. To this day I am grateful that priest taught the Bible as it is written and did not make up things along the way.
The Bible does mention the fact that Mary was married to Joseph and that Jesus had brothers and sisters. Physical intimacy between a husband and a wife is a gift from God and there is no reason to believe this was denied to Mary and Joseph. The Bible mentions that Mary was a virgin at the time Jesus was conceived, but does not say she remained a virgin her entire life and that she did not consummate her marriage with Joseph. Nor does the Bible mention any of the circumstances surrounding Mary’s own birth or mention the possibility that she was conceived of an Immaculate Conception herself.
The notion that Mary and Joseph shared physical intimacy as husband and wife and that other children followed Jesus’s birth appears to be in accordance with everything written in the New Testament and does not take anything away from Joseph, Mary, or Jesus.