That is exactly why I suggest that Mom and Dad sell out and buy a one bedroom condo when the last fledgling leaves the nest...
8^)
My parents began drilling me from the age of about 14 onward, that once I passed the age of 21, I would no longer have any claim to floorspace in their house, and if they deigned to allow me to live with them after that, that my relationship would be that of a renter - nothing more.
They never sold the big four bedroom house, and since we (7) left home, only a couple of us have ever endured the discomfort of living under their roof, even temporarily.
I'm drilling my kids the same way now.