A little while ago a Baptist Chaplin asked if we as Catholics believe that Jesus had two sisters. While I had heard many arguments that Jesus had brothers and sisters from various Protestants I had never heard someone say Jesus had two sisters. These discussions about Jesus’ brothers and sisters are very interesting, but it seems that our Protestant brothers and sisters cannot seem to understand our Catholic teaching of Mary’s Perpetual Virginity.
The Catholic Church is clear in Her teaching that the Blessed Mother was a perpetual virgin. “The deepening of faith in the virginal motherhood led the Church to confess Mary’s real and perpetual virginity.” Jesus’ mother being a perpetual virgin makes it clear that Jesus had no biological brothers or sisters.
The perpetual virginity of Mary is not a recent creation of the Church. The bible in fact seems to support that Mary was a virgin. In the moment immediately before his death, Jesus gives his mother to John and John to her. “Woman, behold, your son! Then He said to the disciple, behold, your mother!” If Jesus had biological brothers or sisters why didn’t they take care of Mary after the death of Jesus?
The early Christians also held Mary to be a virgin. The earliest written record of the belief in the perpetual virginity of Mary I could find is the Protoevangelium of St. James, an apocryphal gospel dating to 149 A.D. While this gospel is apocryphal, meaning it was not considered the inspired Word of God and thus not a part of the Bible, it gives evidence to the early Church’s belief in the perpetual virginity of Mary. By the fourth century many Church Fathers like St. Ambrose, St. Jerome, and St. Athanasius demonstrate that the claim of Mary’s perpetual virginity is well attested to. In 649 the Lateran Council affirmed the truth of the perpetual virginity of Mary.
It was not, in fact, until the Protestant Reformation that the perpetual virginity of Mary was truly challenged by Christians. Some of the reformers, excluding Luther, looked at the gospels and saw frequent reference made to the brothers and sisters of Jesus and claimed the Church’s teaching was wrong. Some members of the early church already noticed the mention of brothers and sisters and had different explanations for them. The Protoevangelium of St. James suggests the reference to children refers to the children of St. Joseph from an earlier marriage. St. Jerome in his work The Perpetual Virginity of Blessed Mary says the claim of brothers and sisters in the gospels claim either these brothers and sisters were either step-brothers of Jesus or were first cousins, the children of Elizabeth, Mary’s sister. Others showed that the terms brothers and sisters was used not only for biological brothers and sisters but also for cousins, close friends or even people from the same town.
While the bible certainly makes mention of brothers and sisters of Jesus in the text, the belief of the perpetual virginity of Mary is still true. Those who hold this teaching to be false fail to realize the early church found no conflict with the term brothers and sisters and the perpetual virginity of the Blessed Virgin Mary. Personally I am inclined to believe the long standing teaching of the Church which originates in those Christians who were only one or two generations removed from the Blessed Virgin and most probably were told of this tradition by those who knew the Virgin, over a very simple and literal (without any consideration for etymology) reading of Scripture that fails to show the Church is wrong in Her teaching. In short a belief in the perpetual virginity of Mary is logical and does not contradict the text of the Bible.
 Catechism of the Catholic Church par 499
 Jn 19:26-27