What does the conversation with the murderers reveal about Macbeth?

Answer 1

The conversation he had with the murderers show that he is still trying to cloak his crime under a veneer of political necessity, by suggesting that the murderers have good reason to hate Banquo and wish him dead. In reality they are hired murderers, who would kill anyone if they were paid to do it. They are quite happy to attempt to kill Fleance, who is obviously not their enemy. So, what is Macbeth on about? He is trying to justify the murder to himself, because he still has enough conscience to think that it is wrong to kill his friend just because his decendants might become kings someday.

Answer 2

They talk about how to go about murdering Banquo, of course. But also, and strangely, Macbeth wants to talk about why Banquo should be murdered, trying to justify it in the eyes of the murderers. The murderers probably don't care, so long as they are hired for the job, but Macbeth doesn't want to admit to himself that he has hired a couple of guns for hire to bump off his friend. He wants it to be a personal grudge between the murderers and Banquo.