This rules out option 1, that Macbeth killed the chamberlains at the same time as Duncan. We have no reason to suspect Lennox of complicity with the murder plot, therefore no reason to doubt what he says here, which is that the chamberlains “stared, and were distracted”, which they could not have done if Macbeth had killed them at the same time as Duncan.

No man’s life was to be trusted with them. So were their daggers, which, unwip’d, we found Their hands and faces were all badg’d with blood Those of his chamber, as it seem’d, had done’t: Macbeth and Lennox come back (with Ross, whom we can suppose has been woken by the commotion) and report the killing of the chamberlains. Approach the chamber, and destroy your sight Macbeth and Lennox go to see for themselves. Tongue nor heart cannot conceive nor name thee! Macduff returns and reports that he found Duncan murdered. Macduff goes to visit Duncan in his chamber. Option 2 is correct: Macbeth killed the chamberlains during act II scene 3, where the sequence of events is as follows: So the way it looks to me, this appears as a plothole. This can't be possible since Lennox went with him (presumably, 'Exeunt Macbeth and Lennox' II.3.72) and murdering the servants in front of a nobleman is likely to elicit some reaction in the very least from Lennox in the confrontation - but he does not mention it nor are we given any hints as to whether Lennox supported Macbeth (if any, he leads the army against him later on). Macbeth murdered the chamberlains after Macduff reports the king has been murdered. So, in my opinion, there is absolutely no chance Lady Macbeth wouldn't have noticed the murdered chamberlains and not say anything to Macbeth about it when she returns after marking them with blood (even if they were under stupor from the alcohol, seeing whether someone is dead or alive is not very difficult) so this seem improbable in my view. However, as we see later in the play that Lady Macbeth has no capacity to actually murder Duncan ('Had he not resembled my father as he slept, I had done't'). Macbeth killed the servants when he murdered Duncan. However, doesn't this appear as a plot hole when we take Lady Macbeth's reaction into account ('Help me hence, ho!')? In Macbeth, at the end of Act 2, Scene 3 Macbeth reveals that he killed Duncan's servants:

Who kills macbeth