They won't be BFFs soon... 2 females in a tank together will turn into trouble and soon.
I would keep them all separated while you get your tank filled in more.. then reintroduce them all at once. As mentioned before- females are just as aggressive as males and naturally do not want to live with other females. But we can make it happen if we densely plant the tanks, and because unlike males- they don't tend to set up a spot for territory in the wild.. so they do run into other females and don't feel the need to attack. All the time.
So fill it up with a lot more plants, medium and high level..
Also keep in mind, even for the most experienced betta keepers there can and at some point does happen on a level, sororities fail. It can happen a week after set up, or a couple years after set up. All it takes is one girl having a bad day.. and they all need to be separated.
Color has nothing to do with it.. those two were most likely the most passive of the bunch.. but once they realize there are only two of them, that will change and they will be attacking one another.
How big is that tank? For some reason it looks smaller then a 10 gallon..