Banquo's primary allegiance is to King Duncan, as he is a loyal and trusted friend to the king. Banquo's loyalty to Duncan is demonstrated when he fights alongside him in battle and remains faithful even when tempted by the witches' prophecies.
He doesn't say. Macbeth even asks him whether or not he hopes his children will become kings and Banquo does not answer him.
So long as he can keep his bosom franchised and his allegiance clear, he will be counsell'd.
Good question. The text is unclear. There is an exchange where Macbeth suggests that he has plans which will augment Banquo's honour and Banquo answers cautiously, "So I lose none in seeking to augment it, but still keep my bosom franchised and allegiance clear, I shall be counsell'd." Did he suspect something? It's a director's call.
No, most countries assume allegiance.
Macbeth says he fears Banquo's wisdom the most because it poses a threat to his plans. He worries that Banquo's intelligence and insight may uncover his own misdeeds and ambitions.
Macbeth is most worried about the prophecy that Banquo's descendants will inherit the throne, as he fears losing his own grip on power and authority. This thought fuels his paranoia and leads to his decision to have Banquo and his son killed.
No logical reason, but then fear is not a logical thing. Although Macbeth says, "My fears in Banquo stick deep," he is not totally clear about why he is afraid of him. Most likely, he is afraid that Banquo knows too much about him, knows what the witches said to him and how troubled he was by it, and as a result may suspect Macbeth of murdering Duncan. He is also annoyed by the prophecy of the "fruitless crown" and the prophecy that Banquo will be the father to kings. To prevent this, Macbeth would have to kill not only Fleance but also Banquo, to prevent Banquo from fathering more children. This prophecy does not threaten Macbeth, yet he feels threatened by it. All of this makes the ball of anxiety which he feels because of the murder focus irrationally on Banquo.
Banquo was created in 1603.
Macbeth kills Banquo in the play and then Banquo's ghost haunts Macbeth.
The ghost of Banquo.
Banquo's son is Fleance.
Banquo's last name was not given.