The New Testament does not mention Mary giving birth to any other children besides Jesus; none but Jesus is described as the son of Mary. Jesus is described as Mary’s “first-born son” (Luke 2:7) but that description does not necessarily imply that she later gave birth to any other children. (See Numbers 3:40,43, where one-month-old males are similarly described as “first-born” when it would have been too early to tell whether or not their mothers would later have any more children.)
The New Testament literally says that the Old Testament patriarch Joseph, the son of Jacob, had eleven brothers. (Acts 7:13,18) However, only one, namely, Benjamin, had the same mother (Rachel) as Joseph. His other “brothers” indeed had Jacob as their father but other women (Leah, Zilpah, Bilhah) as their mothers. (Genesis 35:22-26) Therefore, it is wrong to assume that the “brothers” and “sisters” of Jesus mentioned in the Bible were necessarily the biological offspring of Mary. The fact that Jesus, just before his death on the cross, entrusted his mother to his beloved disciple and he took her into his own home (John 19:26,27) suggests that Jesus was an only child, as does the prophecy of Zechariah:
And I will pour out on the house of David and the inhabitants of Jerusalem a spirit of compassion and supplication, so that, when they look on him whom they have pierced, they shall mourn for him, as one mourns for an only child, and weep bitterly over him, as one weeps over a first-born. (Zechariah 12:10)
