My girls are pretty peaceful, sometimes they do chase one another out of their little territory or spot, but no real fights. They are pretty relaxed most of the time. Tilda is the most aggressive, but she just chases a bit then stops.
Only about 2" so they'll be betta sized. The only thing would be if they started spawning they might get aggressive. They probably won't unless you actually condition them however..
How are your girls? Are they peaceful?