We find one of the most important connections in Luke 1:36, where the same angel who informs Mary that she will bear a Son also tells her, "Elizabeth your relative has also conceived a son in her old age." This same Elizabeth would give birth to a son named John, who would be known to history as John the Baptist (Luke 1:57-60, Luke 1:80).
The exact relationship between Mary and Elizabeth isn't spelled out, but apparently they were cousins, which made Jesus and John cousins. The two of them were clearly aware of each other's ministries, and when John saw Jesus coming to him to be baptized, he exclaimed, "Behold! The Lamb of God who takes away the sin of the world!" (John 1:29).
While it was divinely revealed to John that his cousin Jesus was the prophesied Messiah (John 1:30-34), the fact that John so unhesitatingly accept-ed the truth of this revelation testifies to the fact that Jesus had to have lived a sinless and upright life.
Some apostles were cousins
Although few people are aware of it, at least two of Jesus' apostles also apparently were cousins. We discover this when we compare the lists of the four women who witnessed Jesus' crucifixion as recorded in Matthew 27:56, Mark 15:40 and John 19:25. Comparing these accounts we see that the women included:
• Mary of Magdala or Mary Magdalene (mentioned by Matthew, Mark and John);
• Mary, the mother of Jesus (mentioned by John);
• Another Mary, identified by John as "Mary wife of Clopas" and by Matthew and Mark as "Mary the mother of James and Joses."
This James is generally identified as James the Less, one of the 12 apostles, also called "James the son of Alphaeus" (Matthew 10:3; Mark 3:18; Luke 6:15). "Clopas" and "Alphaeus" seem to be variations of the Aramaic name "Chalphai," which can be transliterated into Greek as "Clopas" and Latin as "Alphaeus."
The 2nd-century historian Hegesippus states that Clopas was a brother of Joseph, Mary's husband and stepfather of Jesus. If true, then this apostle James was a cousin of Jesus.
• Salome (mentioned by Mark), also called "the mother of Zebedee's sons" by Matthew and "His [Jesus'] mother's sister" by John. With Salome and Mary being sisters, their children—Jesus, son of Mary, and the disciples James and John, sons of Salome and Zebedee—were first cousins.
This relationship sheds light on the incident in Matthew 20:21, where "the mother of the sons of Zebedee" asked that her sons, James and John, be given the two most prominent positions in Christ's Kingdom. The request seems quite audacious—but then we realize that the requester was Jesus' aunt, making the request on behalf of His two cousins.
Their closeness to Jesus as family members likely made them think such a request wouldn't be seen as too forward—and also helps explain Jesus' tactful but firm response.
This family relationship also helps us understand why James and John, along with Peter, were the three disciples Jesus seems to have been closest to, asking them to accompany Him at significant times and events (Matthew 17:1-9; Matthew 26:36-37; Mark 5:37). Jesus was evidently close to these two cousins in particular, and obviously enjoyed their companionship. It isn't much of a stretch of our imagination to think they might have grown up together and been friends from childhood.
Jesus' brothers and sisters
The Gospels also show us that Jesus had many half brothers and half sisters who were born to Joseph and Mary. In Matthew 13:55-56 we see that some residents of Nazareth asked: "Is this not the carpenter's son? Is not His mother called Mary? And His brothers James, Joses, Simon, and Judas? And His sisters, are they not all with us?"
This passage names four half brothers —Jacob, Joseph, Simeon and Judah in Hebrew—and mentions His half sisters (plural). Thus Jesus had at least six half siblings—four brothers and two sisters.
During Jesus' life, His half brothers did not believe in Him as Savior and Messiah (John 7:5). Yet, after His resurrection, James became a prominent believer. In Acts 1:14 James, along with his other brothers and his mother Mary, is among the original members of the Church, the same group that received God's Spirit on the day of Pentecost (Acts 2:1-4).
James later became a leader of the Jerusalem congregation. He played a prominent role in the conference of Acts 15 (see Acts 15:13-21). Paul later visited James in Jerusalem (Acts 21:18). In Galatians 2:9 Paul refers to James as a "pillar" of the Church. James also wrote the New Testament epistle that bears his name (James 1:1). Another brother listed above, Judas or Judah (Matthew 13:55), wrote the short epistle of Jude (Jude 1:1).
The fact that these relatives, including half brothers who grew up with Him under the same roof, accepted Jesus as Messiah and personal Savior is also strong testimony to fact that He lived an exemplary and sinless life. And the fact that they became believers after His resurrection is a powerful witness to the reality of that resurrection from the grave.