What key information about the Cadmus family (Antigone's family) is revealed in the opening scene?

In the opening scene of "Antigone," it is revealed that the Cadmus family has suffered a great tragedy, as both of Antigone's brothers, Eteocles and Polynices, were killed in battle. Antigone's uncle, King Creon, has decreed that Eteocles will receive a proper burial and be honored, while Polynices' body is to be left unburied and dishonored. This sets the stage for the conflict that drives the rest of the play.