Mar 3:33 Who is my mother, or my brethren?
Alternative version: Who do I come from? and who is with me?
Christ always used the term translated as "brethren" or "brothers" in the widest possible sense, that is, as the member of the same house or more generally, someone with whom you have a relationship. It indicates a closer relationship than the idea of "neighbor," which Christ uses to mean anyone to whom you are physically near. You can be physically close to someone without have a personal relationship with them.
Mother is the physical source of a house (Jews follow the maternal line) while fathers are the master and protector of the house.
Referring back to Christ earlier references to a house not being divided against itself, Christ is using this opportunity ask what the real meaning of a "house" is under the universal rule. He is asking us if we can see beyond our physical relationships. Just as we are joined into a physical house by the information we share in our DNA, we are also bound into a "house of ideas" with those with whom we share ideas and beliefs.