The Greek tragedies are based on parts of mythological cycles that would have been known to their audiences. In the case of Sophocles' Antigone, the story of the curse on the Theban house was a familiar one, as was both the outcome of the play and the back story.
In another play by Sophocles, Oedipus Rex, we learn of the events immediately preceding those described in Antigone. Because Laius heard his son was to kill his father, when Jocasta, his wife bore a child the baby was sent away to be exposed on a hillside. Instead, the child, Oedipus, survived, and not knowing his own identity returned to Thebes and accidentally killed his father and married his mother Jocasta. When it is discovered that Jocasta is indeed the mother of Oedipus, she kills herself. Oedipus blinds himself leaves Thebes. All this occurs before the dramatic time of the play Antigone.
Creon is Jocasta's brother and Antigone and Ismene are her daughters.