None of Jesus’ brothers believed on Him. Even after Jesus fed the 5000, raised up a man from his sick bed and walked on water, his brothers did not believe Him, the Bible does record this.
Even up to His crucifixion his brothers did not believe Him.
James the brother of Jesus became a believer following the death of Jesus. He went about proclaiming Jesus was God, and was subsequently killed by the Jews – he was thrown down from the top of a temple and then stoned to death.
Let’s think about this, James who was a brother of Jesus did not believe in Him when He was alive in spite of all the miracles He did. He did not believe in Him when He was crucified. What could have influenced James after Jesus’ death that caused him to be a follower and proclaim Jesus at the risk of his own life? If he was just making it up for any reason, would he not have renounced Jesus at the point of death?
Only one answer makes sense – Jesus rose up from the dead. James saw Jesus after the resurrection and hence the change of heart at the cost of his own life!