'Brethren' in the Bible

Then come do his brethren and mother, and standing without, they sent unto him, calling him,

and a multitude was sitting about him, and they said to him, 'Lo, thy mother and thy brethren without do seek thee.'

And he answered them, saying, 'Who is my mother, or my brethren?'

And having looked round in a circle to those sitting about him, he saith, 'Lo, my mother and my brethren!