An argument could be made that Macbeth also murdered Young Siward because Macbeth did kill him, but it was in the final battle at Macbeth's castle. Also, when Macduff hears about the murder of his wife and family, he says, "All my pretty chickens? Did you say 'all'?" (Act 4, sc. 3) which would indicate there was more than just the son that we see earlier in Act 4.
Let's see...King Duncan, Banquo, Lady Macduff, Lady Macduff's son...that would make four murders. And yes, Macbeth is responsible for them all, unless one wanted to somehow blame the witches and Lady Macbeth for setting him onto the course of action that he chose. Ultimately, though, he had free will and could have stopped at any time, or not started with the first murder (King Duncan) that led to everything else.
In addition to all those that Macbeth murdered after the witches prophecies, he also killed Macdonwald, the Scottish traitor, and other invaders of Scotland. Of course, all of these acts were "honorable" because he was defending his king and his country.
*Macbeth kills King Duncan
*Macbeth kills Duncan's two doormen
*Macbeth hires three murderers to kill Banquo
*Macbeth hires the murderers to kill Lady Macduff
*Macbeth hires the murderers to kill Macduff's son along with his other children (unknown how many he had) (this can be determined because Macduff asks if all his pretty chickens were killed which indicates the presence of more than one child)
*Macbeth also killed Young Siward
*Lady Macbeth killed herself (committed suicide)
*Last but not least Macduff kills Macbeth
So more than 9 murders were committed in Macbeth
and all but two of them were Macbeth's fault (Lady Macbeth's death and Macbeth's own death)
- Macbeth Kills Young Siward
- Macbeth kills Duncan
- Macbeth kills Duncan's Servants (2)
- 3 Murderers kill Banquo (hired by Macbeth)
- 3 Murderers kill Son of Macduff (hired by Macbeth)
- 3 Murderers kill Lady Macduff (hired by Macbeth)
- Macbeth Also kills all 3 murderers to cover his tracks (3)
- Lady Macbeth kills herself
- Macduff kills Macbeth
Altogether Macbeth kills 10 people not including the people at the beginning in the war scene.
Here is a list of all the killings...
Macbeth > Young Siward
Macbeth > Duncan
Macbeth > Duncan's Servants
3 Murderers > Banquo
3 Murderers > Son of Macduff
3 Murderers > Lady Macduff (assumed and proven in Ross's speech)
Lady Macbeth kills herself
Macduff > Macbeth
those are all of the ones i have!
there was also the murder of Duncans chambermen who were blamed for the murder of Duncan. Macbeth kills them before they can deny the murder so as to save himself.