I read and listen to people and it just seems that some people do not necessarily care about this. All seven of them started to argue and bicker with each other or... All seven of them started to argue and bicker with (or amongst) one another. Which is correct and is there any time at all when you could use "each other" for more than two? Does it also depend on where you're from?
All seven of them started to argue and bicker with each other or... Though there are many pedants who will argue the above is wrong for there being more than two people, it's idiomatically acceptable. All seven of them started to argue and bicker with (or amongst) one another. This is not a phrasing I would use. If I were to pay attention to there being more than two people in the logic of the statement, I would say: All seven of them started to argue and bicker amongst themselves.
Although it may be idiomatically acceptable, it still sounds funny (at least to me). I could see how just rewriting the second sentence gives it a reasonable standing.
Yeah, the whole singular, dual, plural dynamic is a hard dynamic to keep stable in English since it seems to be a borrow from Latin during one of the "let's make it more like Latin" phases the language has gone through. Just be happy it's not Russian. Russian makes a distinction between singular, plural (less than five), and plural (more than five).
Yeah....they will lose me real quickly on the Russian language. Will have to pack my bags and return home...