Often when a Christian reads the Bible they will get confused by the following verse in the Gospel of Matthew:
Is he not the carpenter’s son? Is not his mother named Mary and his brothers James, Joseph, Simon, and Jude? (Matthew 13:55)
Some translations will switch-out "brothers" for "brethren," which is a more general term.
The primary problem behind the word "brothers" is that it would appear to deny the Blessed Mother's perpetual virginity. This would make it seem that Jesus had biological brothers and that Mary was not a virgin.
Adelphos
All English translations of the Bible rely on the Greek original text. In Greek, the word used for "brothers" is "adelphos."
According to Fr. William Saunders, "In the original text of the Gospel, we find the Greek word adelphos meaning brother, used. However, it does not just mean blood brothers born of the same parents. Rather, adelphos was used to describe brothers not born of the same parents, like a half-brother or stepbrother. The word also described other relationships, like cousins, nephews, etc."
This means that the word in the Gospel of Matthew translated as "brother," could mean any number of familial relations.
It doesn't necessarily mean that Jesus had blood brothers, but that he had other family members, such as cousins.
Fr. Paweł Rytel-Andrianik explains in an article for Aleteia that this was the opinion of the early Church:
[A hypothesis comes from] Hegesippus, an author who wrote in the middle of the 2nd century. According to his theory, “Jesus’ brothers” are the relatives of St. Joseph, or more precisely the sons of his brother, Cleophas, and thus Jesus' first cousins. This opinion is described by Eusebius of Caesarea in his Ecclesiastical History (3.11 and 32; 4.22). This was also the opinion of St. Jerome.
Most biblical scholars agree with this assessment of the situation, as it coincides with other parts of the Bible where the "adelphos" term is also used.
The Church affirms that Jesus did not have any biological brothers, and that Mary was a virgin her whole life:
Jesus is Mary’s only son, but her spiritual motherhood extends to all men whom indeed he came to save: “The Son whom she brought forth is he whom God placed as the first-born among many brethren, that is, the faithful in whose generation and formation she co-operates with a mother’s love (Catechism of the Catholic Church, 501).
While some translations can be confusing, when you dig deeper, the original text does not contradict official Church teaching.
