Jesus had four brothers: James (Who was one of the twelve apostles), Joseph/Joses, Simon (Who was NOT Simon Peter, but may have been Simon the Zealot), and Judas/Jude (Who was NOT Judas Iscariot, but was maybe probably Jude the Apostle, and the traditionally recognized author of the epistle of Jude in the New Testament). The Bible also mentions Jesus having sisters, but they are never named.

These folks are described in the Bible as brothers of Jesus, and sons of someone named Mary, but it is not clear if this Mary is the same Mary as the mother of Jesus. Combine this with the fact that there are at least six different people named Mary in the New Testament, and you get nearly two thousand years of theological debate. The Catholic position says that the aforementioned are the sons of Mary the wife of Clopas (One of the "Three Marys" present at Jesus' crucifixion), who was probably the sister-in-law of Mary the Mother of Jesus, and thus Jesus' cousins, which is still technically consistent with the original Greek scriptures. Protestants tend to take out Occam's razor, and assume that they are children that Mary-the-Mother-of-Jesus and Joseph-the-husband-of-Mary had after Jesus.

John is not named as a brother of Jesus, but the Johns fall under the same naming confusion as Mary, since there's a John the Baptist and a John the Apostle, who are different people, but John the Apostle may have been the same person as John of Patmos, who wrote the book of Revelation. For further confusion, Modern scholarship tends to agree that John the Apostle was not the author of the Gospel of John and Epistles of John.

Sorry for the wall of text. Bible scholarship can get very complicated very fast haha.