1. Macbeth was honest with his wife when he informs her of his new title as "Thane of Cawdor." He refers to the witches as "weird sisters" probably because he doesn't want her know that he is associated with the "evil servants."
Lady Macbeth responds by saying that she thinks Macbeth is playng things off as if everything is fine. By saying "but be the serpent under't", she describes him as someone that lies to make everything appear under control. This doesn't really match the characterization of Macbeth so far in the story which implies that there is something the audience doesn't know about him.
2. The wife was confident about the guests visit. She also seemed prepared and a little cocky about the way her and her husband would handle it.
3. Lady Macbeth. Yes she wants to kill Duncan. No, he isn't sure whether he wants to follow through with Lady Macbeths orders or not. She tells him not to let Duncan see tomorrow.
4. The question appears to answer itself.
