I would use []{} or []{}, as in:
> "they (group B) discussed among themselves"
> //
> //
>
> "they quarrelled among themselves"
> // // []{}
> // //
You could also use :
> // etc.
[]{} would go better with (), as in:
>
> (← probably a bit colloquial)
> ("They quarrelled among themselves.")
And I think would go better with :
> (← probably less formal)
> ("They discussed among themselves.")