Hotel rooms vary in size around the world. A “double” in Paris, as an example, means it holds two people not two beds. Be sure to look at the details when booking. In general, European hotel rooms are quite small. As are New York City rooms sometimes, as compared to other parts of the US.
The same goes for Airbnb or other home sharing sites. Just because it “sleeps 6” does not mean the accommodations are “normal”. There could be couches, etc. involved or all 6 beds could be in the same room so you cannot assume there are separate bedrooms.