Jesus had brothers and sisters and they are named.Matthew 13:54-57 Coming to his hometown, he began teaching the people in their synagogue, and they were amazed. "Where did this man get this wisdom and these miraculous powers?" they asked. "Isn't this the carpenter's son? Isn't his mother's name Mary, and aren't his brothers James, Joseph, Simon and Judas? Aren't all his sisters with us? Where then did this man get all these things?" And they took offense at him. But Jesus said to them, "Only in his hometown and in his own house is a prophet without honor."
Yes, the Lord had brothers and sisters, but why does that require that Mary was also their birth mother? My father has a sister, and his mother gave birth to only one child. Consider what that means. If having a brother and sister means that your mother has to have been the mother of all of them then my father's mother had to have given birth to two children. She did not. Brothers and sisters only refers to the relationship between Jesus and these other people, but it doesn't say anything about Mary's relationship to any of them. This verse also explicitly states that the Lord was the carpenter's son, and yet he was not. At least not as you insist he is a brother and sister to these people.
so you believe another gospel other than that of john 1:1?
Then Joseph committed adultery?
However, that still doesn't answer the question of why it's so important to Catholics that Mary had remained a virgin for her entire life.