It is ironic--that is, funny is an appalling way--that Macbeth and his wife should be planning to treat Banquo with special attention at the forthcoming banquet when both of them hate and fear him and would like to see him and his son dead. It is also ironic that Macbeth and his wife are in such mental harmony, after long years of wedlock, that their motives are so closely parallel that they hardly need to discuss why they should be treating Banquo with special attention. The main reason, as they both understand, is that they don't want to do or say anything that would arouse Banquo's suspicions, although anyone should be suspicious of the motives of people who are being too friendly, too attentive. Macbeth and his wife know that Banquo is an exceedingly intelligent man and that they need to use their utmost cunning to make him feel safe and welcome under their roof. It is ironic that Macbeth is being forced to act the most friendly towards the man he hates most.