Who is My Brethren?

Mark 3:31-35
 
31  There came then his brethren and his mother, and standing outside, they sent to him, calling him.
32  And the multitude sat about him, and they said to him, Behold, your mother, and your brethren outside seek for you.
33  And he answered them, saying, Who is my mother, or my brethren?
34  And he looked around on them who sat about him, and said, Behold, my mother and my brethren!
35  For whoever shall do the will of God, the same is my brother, and my sister, and mother.