At the beginning of the act, whose murder is macbeth planning and why?

The answer to the question above is Banqou and his son, Fleance because Banquo's heirs would become kings, as per the witches' prediction.

At the beginning of the act, Macbeth plans to murder Banquo and his son Fleance because Banquo's heirs would become kings, as per the witches' prediction.