Blood and water
"Blood is thicker than water." Though I didn't always know precisely what they meant by it, this is a saying I heard from relatives on my mother's side throughout my childhood. My great-grandmother Grammar tended to utter these words when she believed family members needed to close ranks against outsiders, or at least think and behave in a manner worthy of the family name. This maxim always seemed to me to have a judgmental quality to it.