Homes were not set up like suburbia. Roman households were a fortress in themselves. Entrance would be through the vestibule, and uninvited strangers would not get any further. Vaccum cleaner or Fuller brush salesmen would be hawking their wares at the market, not door-to-door.
http://www.bible-architecture.info/Housing.htm
Besides the physical (enclosed) structure, there was a distinctive social structure as well. Besides father, mother, and children, there are also other relations and servants. Everyone in the household was subsurvient to the head. If the head converted to Christianity, so did the entire household.
This is the instruction in context regarding entire households accepting or rejecting.