Macbeth Question Can you help ?

This was fate because once Macbeth knew that Banquo's kids would one day become king, and that he should fear Macduff. Banquo's family and Macduff's family become threats to Macbeth. As often is the case when people are a threat to a king, Macbeth was therefore fated to kill Banquo & Macduff's family.