Today's Gospel brings two things to mind: the use of the word 'brother' and the statement about who is his mother.
When reading scripture, it is wise to keep in mind the complexity these books have. We should never take something out of context of the book but also we need to remember that even though they were written by different people and at different times, the Holy Spirit is in charge and ensuring that it has everything necessary for salvation. Eternal salvation is our journey, not a history lesson of Jesus' time.
So we come to the first Gospel item brought to mind in today's reading; the use of the word 'brother'; adelphoi in Greek. Search the meaning and you will find that adelphoi was used to describe male members of the community. In Jesus' time, this doesn't mean just anyone off the street but someone who belonged and participated within the traditions of a tightly knit community.
The second point brought to mind in today's Gospel is Jesus' statement of ‘Who are my mother and my brothers?’. Is Jesus discounting his mother Mary? I would say not. Remember, when reading the Bible, what is being read must be in unison with the complete Bible (all 73 books). How could Jesus discount his mother and thus break the fourth commandment 'Honour your father and mother'?
Jesus is pointing out that being part of the Kingdom of God does not require special blood ties to belong but is open to everyone who does the will of his father, God. Remember, that blessed Mary was not only the mother of Jesus but his best disciple. She followed the path given to her by the Holy Spirit by faith and stuck to it when it could have meant being stoned to death. Jesus nor God would disown such a faithful servant.
image from wau.org