But other of the apostles saw I none, save James the Lord's brother

There is a strong teaching in the Roman Catholic Church that Mary had no other children. However the context of the Gospel Story makes it clear that Jesus had brothers and sisters who were not believers in Him. One of these sons is called James. This James, is shown to be the son of Mary, wife of Joseph, and known well to the people of Nazareth and the region around there. Here are two verses that show the neighbors knew the family:

Matthew 12:46 "While Jesus was still speaking to the crowds, his mother and brothers stood outside, wanting to speak to him."
Mark 3:21 "When his family heard about it, they went to restrain him, because they kept saying, 'He's out of his mind!'"

A little research shows that Joseph's father was named Jacob, also translated James, or Jacobus in South Africa.

Matthew 1:16 "Jacob fathered Joseph, the husband of Mary, who was the mother of Jesus, who is called the Messiah." It is often customary to name a first born son after the father, or grandfather.

Joseph and Mary were commanded by the Angel to name her first child 'Jesus'. When the next child came along, fathered by Joseph, it would be natural to name him either Joseph or James (Jacob).

The apostle Paul writes that he met with an apostle named James, and says he was the Lord's brother.

Galatians 1:19 "But other of the apostles saw I none, save James the Lord's brother". Now notice James is referred to as an apostle. There were 12 apostles chosen by Jesus. Some of the disciples were cousins of Jesus, among them 'James the Less' an apostle and a son of Clopas, the brother of Joseph, Mary's husband. Another James, the son of Zebedee, was also an apostle. There is no account of a James, the half-brother of Jesus being made an apostle!

The scriptures quoted to bolster this theory, are based on the assumption of the word brethren (brother) as being narrow in its application, whereas in many places Jesus himself uses the broader application. In Africa we generally call a cousin, or second-cousin a brother or sister, as they are part of our extended family or tribe.

It is apparent that Mary, Jesus mother, remained in the circle of Believers, as we find her a participant, on the day of Pentecost (Acts 1:14). When care is taken to peruse the Scriptures, I am not sure that the half-brother of Jesus ever became a believer. If the half-brother, James, had become a believer, this would have been a big story, in the book of Acts.

So to sum up in answer to your question:

Mark 6:3 "Is not this the carpenter, the son of Mary, the brother of James, and Joses, and of Juda, and Simon? and are not his sisters here with us? And they were offended at him."

Jesus had 4 half-brothers; the Greek word is 'Adelphos' from the womb of Mary. He had at least 3 half-sisters; Greek = 'Adelphe' female, from the womb, of Mary. If he had but one sister, they would have said so. If he had 2 the word in the Greek would be 'both'. Here they refer to all, being 3 or more who were currently all living in the vicinity of Nazareth at the time, and known to the locals.

In Psalm 69:8 there is a prophetic verse that points to Jesus; saying,

"I have become a stranger to my brothers, And an alien to my mother's children;"

This strongly suggests that Jesus mother would have children after His birth.

Thank you for asking about this!