Family: what's the difference between かぞく and かてい ?
Duolingo teaches you both. There is probably a difference in nuance but what is it?
(Also, I have always wondered about the "No, I don't have a family" sentence because doesn't everybody have one? They use かぞく for that - so does かぞく maybe go more in the direction of "spouse and kids" family, rather than "family of origin"?)
世帯 is a domestic unit (household) and does not have the same sense of 'home' or 'family'. Ex.: 'It is a 5-member household.' Members of a household in the 世帯 sense can be unrelated. There is more focus on the living accommodations rather than the family dynamic or blood relation.
最盛期には五十世帯一六〇人が住んだ。At its peak, there were 50 households with 160 people in residence.
I've heard it used that way in English at times, but not often. It usually (but not always) comes in the form of the phrase "family of [one's] own". It feels somewhat archaic and old-school to my ears, but still happens. Here's a 2014 example:
"My parents got divorced when I was in fourth grade, and it made me pretty jaded about marrying someone ... When I think back on all of it, it actually makes me want to get married. Having a really awesome family of my own and doing everything I can to ensure that none of that ever happens to my children is one of my largest life goals."
Nothing there implies that the speaker lacks parents, brothers, sisters, cousins, etc. In this case the desire for "a really awesome family of my own" implies marriage and children, in a fairly traditional way.
ALSO: None of this is to imply that I am endorsing a narrow definition of family, or what makes any family awesome, or if anybody needs this kind of family to feel happy. This is a language post and I'm pointing out how people use the term.