In the "major themes" section of the "Oedipus the King" study guide under, "The one and the many (also doubles/twos)", the writer contends that Oedipus and Creon were brothers. I have not seen proof of this anywhere in the text. They were brother-in-laws, and in the end, Oedipus turned out to be Creon's nephew, but they were not brothers. In fact, if they were brothers, since Jocasta and Creon were brother and sister, that would make Jocasta Oedipus' sister as as well as his mother. This simply makes no sense.
I have submitted this error to the website but for some reason they suggested that I post the question here.