Matthew 13: 55-56 states “Is not this the carpenter’s son? Is not his mother called Mary? And are not his brethren James and Joseph and Simon and Jude? And are not all his sisters with us?” Reading this through 21st century American glasses would imply that Jesus did have brothers and sisters. To really understand what this meant you would have to put on your 1st century Jewish glasses. Jesus didn’t speak English or Spanish or Italian; Jesus spoke Aramaic and in Aramaic there is no word for cousins. The word for brother and sister was also used when referring to cousins. This would explain the above passage and several other passages in the Gospels referring to Jesus’ brothers and sisters.
This can also be looked at in comparison with modern cultures. In many present day cultures the word cousin, uncle, brother, aunt, etc aren’t used only to describe ones biological cousin, uncle, brother, aunt, etc. Cousins, who grow up together and are very close, many times refer to each other as brother and sister. A father or mother may have a very close family friend that the children of the household refer to as Uncle. This interchanging usage of terms is seen from Latin cultures of Europe and Latin America to countries such as India. The point here is that even modern day cultures don’t use the term brother or uncle solely for referring to a brother or uncle. The usage of these terms is very flexible and this is how they were used in Israel 2000 years ago.
How do the various Churches interpret these passages? The Catholic, Orthodox and various Apostolic Churches of Africa and the East are the only Churches that historically can be traced back to the Apostles. These Churches which believe and agree on 99% of the same doctrine and dogmas all interpret the biblical passages referring to Jesus’ brethren to mean cousins. Think about it, the above Churches that were taught by Jesus and the Apostles, have always interpreted these passages to be cousins, since the apostolic era.
Not until the 16th century did various Protestant groups start interpreting these passages to mean biological brothers and sisters. Even some of the Protestant reformers such as: Martin Luther, Huldrych Zwingli and John Wesley believed that Mary remained a virgin her whole life. Who do you think would have a better understanding of these verses (and the bible in general), the Churches that were founded by Jesus Christ and the Apostles (which have been consistent in their teaching for 2000 years) or the 40,000+ Protestant groups which are constantly disagreeing and separating from one another (most of which are less then 200 years old)? It’s like the game of telephone, as a message constantly changes hands from one group to the other it gets more and more distorted. If one wants to know true Christianity one must go back to the writings of Early Church Fathers (the Christian leaders who were taught by the Apostles) and see what they believed; what they believed is what the Catholic Church believes and teaches and has so for 2000 years.