DH's family dropped in one day unannounced and I told them they could sit out on the porch and wouldn't let them in cause the house was messy. The whole family now gives me a day's notice. Just try something like that - tell them you're busy, the house isn't in a state for the, and have a chat outside on some chairs. Just let them know that if you get warning, then you'll be able to be ready for them. After all, there's a lot of napping happening at this stage of your pregnancy!