We know what Macbeth and Lady Macbeth *do*; what they feel may be up for interpretation depending on how we read what they do and say. For instance, we know that Macbeth murders the guards as they are starting to wake from their drugged state, and says that he's done it out of his love for the king (who could refrain, that had a heart to love, and in that love, courage to make his love known). We also hear Macbeth say "I do repent me of my fury" in explanation for his apparently rash act of killing the guards. But what does he feel? Guilt, definitely, but also borderline panic. His "fury" was probably fear that the guards would start to speak, and cast reasonable doubt on whether or not they were actually guilty of the crime the Macbeths were trying to frame them for. We also know Lady Macbeth faints just as Macbeth is in the midst of rationalizing his actions. Has she fainted because she has had a long night? Some say so, and further suggest that this marks the beginning of the Lady's weakness. It is possible that the night has been too much for her--she probably hasn't eaten, and she certainly hasn't slept; however, the timing of her fainting spell is simply too perfect, especially given that before she faints she draws attention to herself saying, "Help me hence, ho!" Were this a genuine fainting spell, she would be incapable of such a long utterance. So my reading of her action would be that she's seen her husband on the verge of bumbling the whole thing and she takes a dive--so to speak--to take the focus away from him. If this is the case, then at this point in the play she is still the one in control: he acts on impulse while she calculates their moves.
Of course, they need to pretend that they are as shocked as everyone else. Macbeth even goes so far as killing the king's guards in order "to find justice". Macbeth does feel remorseful and guilty about the crime. At the end of scene two he wishes that he "Wake Duncan with thy knocking! I would thou couldst!" This shows how guilty he feels.
Lady Macbeth doesn't feel the same way. She mocks Macbeth's reaction, calling him unmanly. From this, one can see that she thinks that this murder is just business.
Macbeth has committed the crime, but has not stopped thinking about it. His speech symbolizes the fact that he understands that the assassination will mean eternal damnation for him, and an unavoidable afterlife judgement. After having come back to his room from that of Dunacan's, Macbeth faces an anxious Lady Lacbeth, who was worried about the success of their hatched plot. Macbeth assures her that the deed had been done, yet his expressions and his words after that make his guilty conscience crystal clear to the audience. 1) He could not say 'Amen' when one of the chamberlains woke up in his sleep and said 'God bless us'. This for him, and the audience alike, symbolizes his regret. 2) He had forgotten to place the daggers near the drunk nd drowsy chamberlains, as his wife had instructed him in his fit of fear of impending repercussions. 3) He said that even after washing his bloody hands, there would be no effect. As it would make the 'multitudinous seas incarnadine' and 'make the green one read', implying that his deed had left a lasting impression and could not ever be cured/compensated for. 4) There is a knocking hear towards the end of the scene, when Macbeth says that he wished the knocking would wake King Duncan up. 5) He refuses to go and keep the daggers near the chamberlains as he 'dared not' look at King Duncan's face again. He was over ridden with such fear and uncertainty.
Lady Macbeth's reaction is entirely different and is worth noting, as it changes towards the end of the play when she is over ridden with undeniable guilt. 1) She is anxious of the outcome of the deed and awaits her husband's return hoping everything had gone according to the plan. 2) When Macbeth starts telling he rof the incidents that took place during the deed, she says that they must not think so much, because it would only disadvantage them. 3) When Macbeth refuses to go and keep the bloody daggers near the chamberlains, she compares him to a child, who is scared of pictures and dead objects(things that will never come to life). 4) She again plays the more dominant role in their relationship, and instructs him to clean his hands and change into his night gown, symbolizing her innate strength and lack of moral scruples.