Make sure you have LOTS of plants for them - the more stuff you stick in there, the less likely they are to fight. You want to break up their line of sight as much as possible, so the bigger, leafy plants are the way to go.
Ones like this:
and you want cover at the top too so they can get air. Some females will chase away any other female when they go to the surface. you can use real floating plants but I use plastic plants by tetra. If you take off the plastic bottom part, their plants will float.
These are the ones I have.
I just stick them in there horizontally and they float at the water surface.
I also have a few of these stuck on the side of the tank.