I agree with the above answer as far as Hecate and Donalbain are concerned. Maybe three murderers are unnecessary and the actual murder of Banquo doesn't have to be shown. One murderer could report what happened, as is done in the play.
I also believe that Malcolm could be eliminated. He does not have to be shown discussing with his brother their mutual fears for their lives and their intentions to flee to foreign realms. This is covered in some of the other dialogue. Leaving Malcolm out would strengthen Macduff's role. When the English army reaches Birnam Wood, any officer might order the men to cut down branches. It would be understood that Malcolm fled to England, raised an army, and returned to Scotland with Macduff. Malcolm doesn't actually do much when they reach Dunsinane; it is Macduff who kills Macbeth.
Lady Macduff and her son could be eliminated. Their murders could be reported to Macduff in England, as it is now. Eliminating Lady Macduff and the boy would also eliminate their murderer.