Final answer:
Macbeth's doubts and moral hesitation are the main obstacles to executing the plans he and Lady Macbeth have devised, as he struggles with loyalty, the consequences, and the ethics of their actions.
Step-by-step explanation:
The primary problem standing in the way of Lord and Lady Macbeth's plans is c. Macbeth's doubts and lack of desire to do it. Throughout the play, Macbeth is plagued by hesitation and moral quandaries, affecting his ability to carry out their plans with decisiveness. Lady Macbeth attempts to encourage Macbeth, asserting their success if they have the courage, while Macbeth contemplates the repercussions of their actions, fearing they might return to plague them. Even after deciding to commit regicide, Macbeth's guilt is evident, and his reluctance stems from a range of reasons including loyalty, fear of consequences, and the immorality of their plot.