Question

Why does Macbeth pay killers to murder Banquo and Fleance

Answer 1

I think it is Banquo and his heirs have a claim to the throne.
I also found this...Macbeth, aware of the threat Banquo and his son pose to his new throne, plans to have them murdered. When Banquo goes traveling, Macbeth sends three men to kill them. Banquo and Fleance are ambushed and Banquo holds the assailants off so his son can escape. The murderers return to Macbeth and report their failure to kill Fleance. Macbeth later meets the Three Witches again and is shown a vision of a long line of kings descended from Banquo.