Hence you share a biological and social relationship with your … half sibling. Step-brother/Step-sister: You are not related to your Step-Sibling in a biological way. Your mother/father is married to one of the Step-Sibling's parents and this is the basis of this social relationship.(A Half-Sibling shares one parent biologically; a Step-Sibling is by virtue of one parent each entering a marriage, with no blood relation. step-sibling is a sibling who is rel … ated to you only by marriage of parents. In other words, your mother or father marries somebody else who already has children. Those children would become your step-siblings, since there is no mother or father in common between you and them. 20 people found this useful.