A family of four doesn’t need four kitchens and four bedrooms, so not every cost scales linearly as a household increases in size. Some things are also cheaper in bulk than if you are just buying enough for one person. I do think a family of four probably needs more than twice what a single person needs, however, but I am no expert on this. In any case, housing costs have drastically outpaced wages and safety nets, which is massively evident by all the homeless camps everywhere.