Even assuming that people started having four children "for the human race to survive" (a wacky thought in itself) what would prevent a family from having a com

Even assuming that people started having four children "for the human race to survive" (a wacky thought in itself) what would prevent a family from having a compound of two or three tiny homes? At some point you would need so many tiny homes you wouldn't have much cost savings. But seems totally doable to have pair of homes or trio of homes, with, e.g., kids sleeping in one and parents in another, connected by common deck/porch.