If you are referring to "chorus characters" as characters who act as a unified whole (similar to the role of the chorus in Greek plays) then the three witches would be the chorus characters in Macbeth. The three act in unison when giving Macbeth and Banquo the predictions for their future. They also continue to plot future events. When Hecate enters the play, she is angry with all three witches for conspiring together and telling Macbeth information that he should not know. Throughout the play, the witches serve as a force for challenging Macbeth's sense of morality and righteousness. So, they serve a similar role in Macbeth as the chorus does in Greek plays.