There has been much discussion through the centuries as to the exact relationship of these men to Jesus. So the question remains, did Jesus have siblings? Three principal views have been advanced:
(1) that they were Jesus' actual siblings/brothers, that is, half-brothers, sons of Joseph and Mary (and therefore younger than Jesus);
(2) that they were His stepbrothers, that is, children of Joseph by a previous marriage (and thus all older than He and not His blood relatives at all);
(3) that they were the cousins of Jesus on the mother's side, according to some, or on Joseph's side, according to others.
Three views about Jesus' siblings
Those who hold the first view argue that this is the most natural way to understand the various references to these brothers; also that this is the most obvious intent of Matthew 1:25 and Luke 2:7.
Those who hold the second view argue that family ethics would not permit younger siblings to taunt or otherwise meddle with an older brother as Jesus' brothers taunted Him (see Mark 3:31; John 7:3-4). They point out further that the fact that Jesus left His mother in the care of the apostle John (John 19:26-27) rather than with one of His brothers strongly implies that Mary had no other children.
The view that these brothers were the cousins of Jesus on Joseph's side is based on pure conjecture. That they were cousins on Mary's side is based on the unproven identity of "Mary, the wife of Cleophus" with the sister of Mary (John 19:25; Mark 15:40), and on the unproven identity of "Clopas" with Alphaeus (Mark 3:18).
Jesus' brothers, sisters & mother
Jesus' siblings are mentioned as accompanying Jesus and his mother to Capernaum after the marriage at Cana (John 2:12). Later Mary and these brothers are recorded as seeking an audience with Jesus (Matthew 12:46-50; Mark 3:31-35; Luke 8:19-21). Toward the end of Jesus' ministry, His brethren are mentioned as urging Jesus to prove His Messiahship, which they themselves doubted (John 7:3-5). That they were later converted is clear, for they are described in Acts as uniting with the disciples and others in "prayer and supplication" prior to Pentecost (Acts 1:13-14). Paul implies that they were all married (1 Corinthians 9:5).
Many commentators hold that the author of the epistle of Jude, who identifies himself as the "brother of James," was one of these brothers (Jude 1). It is also generally believed that the leader of the church at Jerusalem was James the brother of Jesus, (see Acts 12:17; 15:13). This seems to be confirmed by Paul's reference to his visit to Jerusalem, in which he states that he saw only Peter, and "James, the Lord's brother" (Galatians 1:18-19).