How are nobles (Macbeth, Malcolm, Banquo, Lennox etc.) represented in Shakespeare's Macbeth?
The nobles that we meet, with the exception of Macbeth, are all represented as fairly honest, loyal men. Initially, even Macbeth is presented in this way, as he is rewarded for his courageous service to the throne in the battles against the rebel Macdonwald and with the king of Norway's army. Duncan lauds Banquo, too, for his services in these clashes. Ross, too, is trusted by Duncan, and happily tells Macbeth of his reward for his excellent valor: Duncan has given him the title, Thane of Cawdor, since the old Thane was a traitor. The only nobles we hear of who are really guilty of wrongdoing (besides, later, Macbeth) are Macdonwald and the Thane of Cawdor, and Macbeth kills the first in battle while the other is executed for treason almost as soon as the play begins.
Though Macbeth's loyalty falls to his pride and ambition, Banquo's never does. He does enjoy the idea that his descendants will be kings, but he is unwilling to do anything dishonest or immoral to make it happen. Lennox identifies Macbeth as a "tyrant" and strongly suspects that he killed both Duncan and Banquo to achieve and maintain his position (3.6.25); his anger and indignation paint him as loyal and honorable as well. Further, Ross later laments the current state of Scotland with Lady Macduff, showing that he, too, is a Scot loyal to the country and not its awful ruler. Finally, Malcolm, too, is likely the most honest as he never tells a lie until he does so to test Macduff's honesty. Both turn out to be honorable men with Scotland's best interest at heart, and they determine to wrench it from the greedy Macbeth's grip.