All scriptural references are from the Darby Translation, unless otherwise noted
Many believers don't realize that Jesus Christ (a.k.a. Yeshua Messiah) was not an only child when he walked the earth. Although he was the firstborn, he wasn't the only born. He also had at least one cousin as well. This essay will discuss all of the Messiah's human relatives as spoken of in Scripture.
JOSEPH & MARY
Both Joseph and Mary were descendants from King David (Matthew 1:6-16, 20 and Luke 1:27, 3:23-32). If you look at all the names in both of these lists, you'll see that they aren't all identical, though both come from the line of David. Both lists mention Joseph, neither mentions Mary. This is because, when it came to family lineage, it was considered to be through the father, even if it included the wife's family. At any rate, Jesus' human existence was through the line of David in both cases. This is to fulfill prophecy that states Jesus would come from the stump of Jesse (Isaiah 11:1, 10), who was David's father (Ruth 4:22). Joseph was a common carpenter (Matthew 13:55). When Joseph and Mary were betrothed, the angel Gabriel appeared to Mary to give her good news: She would be the human mother of Jesus (Luke 1:26-33). Mary was amazed and inquired more about the matter (Luke 1:34). Gabriel answered her questions and reminded her that even her aged cousin, Elizabeth, had conceived by the miracle of Yahweh (Luke 1:35-37). Mary accepted the circumstances, after which Gabriel departed (Luke 1:38). Mary and Joseph had not yet married when she became pregnant with Yeshua (Matthew 1:18). At first, Joseph didn't believe Mary's explanation of her virgin pregnancy, thinking she had actually been unfaithful to him. As a result, he decided to end the engagement quietly, so as not to make her a public spectacle (Matthew 1: 19). Although they weren't officially married yet, a betrothal was a binding contract for marriage; the couple belonged to each other and no one else. Therefore, couples were required to officially divorce if they chose to cancel their weddings. The fact that Joseph wanted to do this quietly shows how much Joseph loved her, because according to Jewish law, a woman who committed adultery was to be put to death (Leviticus 20:10). Because Joseph was planning to secretly divorce her, God sent an angel to confirm to him that Mary was indeed an honest woman (Matthew 1:20-24). At that point, Joseph decided to take Mary as his wife. Although married to her, Joseph did not consummate the marriage until after Yeshua was born (Matthew 1:25). Yeshua Messiah's human birth occurred during a time when a census was decreed by Augustus Caesar . The citizens were required to travel to their hometowns to be registered. This meant Joseph and Mary needed to travel to Bethlehem, because they were of the house of David, located in Bethlehem (Luke 2:1-5). Since the city was filled with fellow travelers, there were no rooms available for rent. Therefore, they took shelter in a barn, where Mary went into labor and gave birth to our Saviour, and laid him in a manger for a bed (Luke 2:6-7). Later that night, angels appeared to local shepherds, informing them of Christ's birth and where to find him. The shepherds excitedly went to find this newborn child, and found him in the manger (Luke 2:8-16). Upon their arrival, they told of their experience with the angels to all who were there, and Mary treasured their words in her heart (Luke 2:17-19). Joseph and Mary took Yeshua to the temple in Jerusalem to get him circumcised at the age of eight days old, in line with the Jewish law (Luke 2:21, Leviticus 12:2-3), and later Mary went for her purification, dedication, and animal sacrifice according to the law (Luke 2:22-24, Leviticus 12:4-8). At this time, a devout, aged man named Simeon was guided by the Holy Spirit to find them at the temple (Luke 2:25-27). Simeon prophesied about Yeshua, and blessed them (Luke 2:28-35). Some time after Christ was born, evil king Herod found out and tried to kill him. Yahweh thwarted Herod's efforts by sending an angel to Joseph to instruct him to take Mary and the child to Egypt to escape the murder. The family remained in Egypt until Herod's death, when the angel informed them they could return (Matthew 2:13-15, 19-21). However, because Herod's son, Archelaus, came into power, Joseph and Mary decided to live in Nazareth after having been warned in a dream (Matthew 2:22-23). Yeshua grew up with Joseph and Mary, becoming strong and filled with godly grace (Luke 2:40). In Yeshua's adult life, Joseph and Mary were well known as his parents (Matthew 13:55, John 1:45). Apparently, Mary was widowed before Yeshua was killed, for he gave Mary into the care of his disciple before he died (John 19:25-27). Mary was on the scene of the Messiah's murder (Mark 15:40, John 19:25). Mary and her other sons were also present when a large group came together to pray some time after the Messiah's ascension (Acts 1:13-14).
According to Scripture, Yeshua Messiah had human half-siblings through Joseph and Mary. His brothers' names were James, Joseph/Joses, Simon and Judas (all were common names back then) (Matthew 13:55, Galatians 1:19, Jude 1:1). A reference to sisters is also mentioned (Matthew 13:56, Mark 6:3), and one particular verse seems to be referring to one sister as being named Salome (Mark 15:40).
JOHN THE BAPTIST
John's parents were Zechariah and Elizabeth, an aged couple. Zechariah was a priest in the nation of Israel and Elizabeth was a barren woman (Luke 1:5-7). One day, as Zechariah was performing one of his priestly assignments, the angel Gabriel appeared to him. Zechariah was initially frightened by this surprise, so the angel calmed his fears. Gabriel told him that his wife would bear him a son, who was to be named John (Luke 1:8-13). John was to become a Nazirite (which is not the same as a Nazarene, compare Luke 1:15, Numbers 6:3-4 )*. John was assigned to direct people back to Yahweh's Kingdom, and he was to be the foretold Elijah to come, (Compare Malachi 4:5-6, Luke 1:16-17, Matthew 11:13-15, 17:12) as well as the foretold voice in the wilderness (Compare Isaiah 40:3, Matthew 3:3, Mark 1:1-3). Zechariah thought this was incredible, and voiced his doubts to the angel. Because he doubted Yahweh, Zechariah was rendered mute until the actual birth of John occurred (Luke 1:18-22). Soon, Elizabeth did indeed become pregnant, and she kept herself out of the public eye for five months (Luke 1:24-25) It was during her sixth month that the angel Gabriel appeared to Mary and spoke to her regarding her human motherhood for the Messiah (Luke 1:26-38). Here Gabriel refers to Elizabeth as Mary's cousin (Luke 1:36) (WYC, KJV), thereby showing a blood relationship. Mary was thrilled and immediately went to visit Elizabeth (Luke 1: 39-40). When unborn John heard Mary's greeting upon her arrival, he leaped in Elizabeth's womb (Luke 1:41-45). Mary stayed with Elizabeth for about three months before returning home (Luke 1:56). Soon,Elizabeth gave, birth to John. The eighth day after birth they went to perform the circumcision ceremony on him and to officially name him. Once he was officially named, Zechariah's powers of speech returned to him (Luke 1:57-64). John continued to grow and become strong (Luke 1:80). Later, in the fifteenth year of Tiberius Caesar's reign and Pontius Pilate was governor of Judea, God's declaration came to John (Luke 3:1-2). As a result, John performed baptisms in the Jordan River in symbol of repentance of sins. This was in fulfillment of prophecy (Mark 1:9, Luke 2:3-6).
Other than these references, we haven't found any other evidence of Yeshua's human relatives in the Bible.
*A Nazirite was a person who was set aside especially for Jehovah's / Yahweh's service. It could be a male or female. During the period set aside for Nazirite service, the person must abstain from intoxicating drinks, eating neither grapes nor anything made from grapes, nor cut his/her hair and must not touch any dead bodies including those of family members. (Numbers 6:2-12). A Nazarene, on the other hand, was simply a resident of the city of Nazareth (Matthew 2:23).