In Mark 10:35-45, Jesus and his followers had reached the city of Jerusalem. Two of his disciples, who were also brothers, asked Jesus if they could sit on each side of Christ once he began his rule of his kingdom. The two brothers, James and John, were also mentioned again in Matthew 20:20-28. This account of the request to have James and John sit next to Christ also mentions their mother. Their mother is also reported to have made the same request, wanting her sons to have important roles in God's kingdom. While the Bible speculates who exactly James and John's mother was, John 19:25 hints that this woman might be Jesus's aunt, meaning that James and John were most likely Jesus's cousins.
The Bible also makes reference to figures who are identified as Christ's brothers. Mark 6:3 names Christ's brothers as James, Joses, Judas, and Simon. James and Joses appear again in Mark 15:40. This verse references James and Joses as the sons of Mary, who was one of the women present for Christ's crucifixion.
Versus in both Luke and Matthew, specifically Matthew 13:55, mention all four men by name. The goal of versus such as Matthew 13:55, Matthew 1:25, and Luke 2:7 was to show that these four men were the younger half-brothers of Christ. While Christ was the son of God, James, Joses, Judas, and Simon are the natural sons of Mary and Joseph born after the birth of Christ.
The roles that Jesus's siblings took as significant leaders are also mentioned numerous times in the Bible. All four of Jesus's brothers and his unamed sister are named in John 2:12 as accompanying Jesus and Mary to Capernaum after the marriage at Cana. Jesus's brothers are then referenced as seeking an audience with Jesus in versus of Matthew, Luke, and Mark. The Bible also references James as the leader of the church in Jerusalem. One of the other brothers, though not named, is also hinted at as being the author of the epistle of Jude.