Question

what was the first obstacle of Macbeth's path in becoming king​

Answer 1

After Macbeth and Lady Macbeth succeed in their plan to kill King Duncan, even though Macbeth knows his only motive is his "vaulting ambition" (1.7.27), Macbeth then worries that his best friend Banquo may betray him because only Banquo knows what the witches have prophesized for Macbeth: he will be King . Secondly, Macbeth is concerned about the witches' prophecy for Banquo: that his sons will be kings.