The "Brothers" of Jesus = Sons of a Different Mary
The first and most important reason for concluding that the "brothers" of Jesus are not children of Mary is also the most often overlooked. It is this: The Gospels themselves explicitly state that the so-called brothers of Jesus are in fact the children of another woman named Mary.
In order to see this clearly, all we need to do is compare the identities of the “brothers” of Jesus in the account of Jesus’ ministry in Nazareth with the accounts of the people present at his crucifixion and burial. For the sake of convenience, I will focus on the evidence in the Gospel of Mark, paying close attention to the names of Jesus’ “brothers”:
He went away from there and came to his own country … And on the Sabbath he began to teach in the synagogue; and many who heard him were astonished, saying, "… Is not this the carpenter, the son of Mary and brother of James and Joses and Judas and Simon, and are not his sisters here with us?" (Mark 6:1-3)
And Jesus uttered a loud cry, and breathed his last… There were also women looking on from afar, among whom were Mary Magdalene, and Mary the mother of James the younger and of Joses, and Salome, who, when he was in Galilee, followed him, and ministered to him. (Mark 15:37, 40—41)
On the one hand, the Gospel of Mark indisputably identifies 'James" and “Joses” as two of the “brothers” (Greek adelphoi) of Jesus (Mark 6:3). As any Greek dictionary will tell you, the most common meaning of the word “brother” is the same as in English: "a male from the same womb."26
On the other hand—and this is crucial—the Gospel of Mark also provides solid evidence that the same two men, “James” and “Joses,” are the sons of a different woman named Mary. This other Mary is mentioned three times in the account of Jesus’ crucifixion, burial, and resurrection. At the crucifixion, she is called “Mary the mother of James the younger and Joses” (Mark 15:40). At Jesus’ burial, she is called “Mary the mother of Joses” (Mark 15:47). On the morning of the resurrection, she is called “Mary the mother of James” (Mark 16:1). Who is this woman? Obviously, Mark would never refer to the mother of Jesus as “the mother of James and Joses,” or “the mother of James,” or “the mother of Joses,” especially when he has already referred to Mary as Jesus’ “mother”