Same Womb

The idea Mary was an ever virgin who never had children after Christ is a false teaching, Mary did have other sons and daughters. The common argument for the teaching is the word brother meant relative.

The word brother, greek adelphus, means from the same womb. It is used in the same generation of physical brothers or of distant generations of relatives from a common grandmother. It means from a common womb.

Some argue James the Lord's brother came from Joseph and a previous wife. This is found in the gnostic works such as the Protoevangelum of James. 

It would be wrong to use the word adelphus or brother in this case since Jesus and James would have come from different women and therefore different wombs. Also, they didn't have a common father. They could only be called brethren if born after Christ in this case, since Christ was not from a man but the Holy Spirit. They could only have a common parent if the brothers were born after Christ with Mary their mother.

The scriptures also say they lived in the same house as Jesus and Mary , this would imply they weren't just relatives, but actual brothers in the same family. Relatives like Mary and Elizabeth lived in different houses.