Answer: The correct answer is : Because he is the father of his own siblings.
Explanation: Oedipus should fulfill a prophecy about his life:
would be king of Thebes
he would kill his father, Layo
he would marry his mother, Yocasta, with whom he had 2 sons and 2 daughters
Yocasta ends with her own life, Oedipus blinds himself and asks his brother-in-law Creon to let him go to exile and take care of his daughters. Oedipus' family was cursed because of his father.