They are all used to battles, and they all possess the fighting spirit. Macbeth and Banquo first show up at the beginning of the play from the battle against Norwegians in which they were successful. Everyone praises them for their valiance. Macduff is also capable of being a great warrior, such as when he kills Macbeth, as the end of the play shows.
They all exhibit confusion and have difficulty choosing a path to follow. Macbeth unsuccessfully grapples with his unchecked ambition, intensified by the witches' prophecy. Banquo's mind is also fixed on the witches' prophecy; however, he does not do anything about it, unlike Macbeth. And, Macduff exhibits tension between his duty as a husband and a father and his responsibility to save the country from a cold-blooded tyrant.
Good question. They are all warriors, and warriors of great power. They are brave and battle-tested. They all believe in omens or signs that in part determine their fate or safeguard them from danger. They all have to deal with guilt over what they do, and all are concerned with what it means to be an honorable man.