>>> All Barbs need to be in groups of 6+.
This is another common piece of advice I would put a question mark, or at least a qualifier, against.
Whilst it is most definitely true in the case of most barbs seen in the trade, I suggest that in certain cases, it is not.
My own, (40 years +), experience with Barbs, and I mean Barbs in the traditional broad sense, states that, for example, P. titteya, the Cherry Barb, works fine as a male and 1 or ideally 2 females in most size tanks is good. 2 males in almost any size tank leads to issues, small scraps, but issues none the less.