In Macbeth, whom do Macbeth and his wife plan to take the blame for Duncan's murder?
In Lady Macbeth's plan to murder King Duncan--and it was she who worked out all the details--Duncan's grooms (his attendants) were to be blamed for his murder. She would drug their drinks so that they would sleep, and then she would lay out their daggers for Macbeth to use in killing the king. Macbeth was to commit the murder, smear the sleeping grooms with Duncan's blood, and leave the daggers at the scene. Thus it would appear that these men in Duncan's chamber, covered with Duncan's blood, had committed the deed.
Her plan unfolded with two exceptions. Macbeth forgot to leave the daggers behind, so Lady Macbeth had to return them. After Duncan's body was discovered, the king's sons, Malcolm and Donalbain, ran away, fearing reasonably that they, too, were in danger. Because they had fled the scene without explanation, the guilt for Duncan's murder then fell on them. Macbeth and Lady Macbeth certainly didn't argue about this misconception.
It was Lady Macbeth who chalked the blueprint of the murder of Duncan. In act1 sc.7, she also told Macbeth how she was going to implicate the two chamberlains of Duncan in the crime. First, she would make them unconscious with 'wine and wassail'; and then the blame of the heinous act would be conspiratorially imposed upon them:'.....what not put upon/His spongy officers, who shall bear the guilt/Of our great quell?' According to her plan, Macbeth was supposed to leave the daggers of the grooms as stained with blood, and the grooms themselves as smeared with the same, so that they would be easily detected as the killers of the king. When Macbeth returned, after the murder, to Lady Macbeth, she could see those bloody weapons still with her husband. Since Macbeth refused to revisit Duncan's chamber, Lady Macbeth herself went back to do the needful. In act2 sc.3, when Duncan's sons, Malcolm and Donalbin, decided between themselves to escape to England and Ireland respectively, for their safety, the suspicion and blame came to fall on them.