Agree another female may help.
They're not bullying each other in the sense of aggression. Male cherry barbs want to breed all the time, and will chase females constantly to try and make them drop eggs.
It's better to have more females than males, so the same female isn't being bothered all the time.
Lots of plants and hiding places help a lot.
I"ve been keeping cherry barbs for many years. Right now I have 2 males and 4 females and lots of plants in a 20 gal. Everyone seems fine with this, although the males can certainly be a pain!
