The main way that Macbeth betrayed both Banquo and Macduff was by killing the king. Macduff was particularly affected by Duncan’s murder in Act II, Scene 3.
Up, up, and see
The great doom's image! Malcolm! Banquo!
As from your graves rise up, and walk like sprites,
To countenance this horror! (enotes etext pdf p. 34)
When Macduff finds out that it was Macbeth that killed Duncan, he is angry. In Act III, Scene 4, Macduff skips the banquet. He begins to make plans to unseat Macbeth and return the kingdom to the rightful heir, Malcolm in Act III, Scene 6.
Is gone to pray the holy King, upon his aid (p. 56)
Macbeth’s betrayal of Banquo is much more personal however. They seem to be great friends in Act I. Macbeth is obsessed with the prophecy of Banquo’s sons being king and thinks nothing of murdering Banquo when he begins to get suspicious in Act II, Scene 1.
Our fears in Banquo
Stick deep, and in his royalty of nature
Reigns that which would be fear'd. (p. 42)
Of course, Macbeth does feel guilty about murdering Banquo. At first, he seems fine and "takes joy in learning that Banquo is dead, because he cannot produce any more sons" (enotes summary, Act III, Scene 3). In Act III, Scene 4, he sees Banquo’s ghost and responds with what seems like guilt.
Blood hath been shed ere now, i’ the olden time,
Ere humane statute purged the gentle weal;
Ay, and since too, murders have been perform'd
Too terrible for the ear. (p. 51)
Macbeth is well aware of the fact that he betrayed both Banquo and Duncan. Lady Macbeth seems to have more guilt about Duncan than Macbeth. It is after the murder of Banquo that Macbeth really begins to deteriorate.
For the full text pdf, read here: http://www.enotes.com/macbeth-text
For more summary, read here: http://www.enotes.com/macbeth/act-iii-summary-analysis