Sounds like maybe they a hand with the cleaning? Maybe a family working bee and a huge spring clean. They don't have to know it is about bub arriving, they can just think you guys are giving them a hand......
If that's not a possibilty then i guess you'll have to do s bathsheba suggested and grin and bear it. When he is older you can always send him with a bag of snacks/food that is more to your liking!