step siblings can be one of these 의형제(義兄弟) = step brothers 의남매(義男妹) = step brother and step sister 의자매(義姊妹) = step sisters 의형(義兄) = step elder brother 의제(義弟) = step younger brother 의자(義姊) = step elder sister 의매(義妹) = step younger sister Someone calls step brothers as "의붓형제", but "의붓형제" is no a correct word.

We called it 이복형제, 이복 means different parents(but literally it means different belly).