Ok. Rehoming them to something larger aside (unless that is an option), my only other thoughts are:
1. Try moving decor around to allow for more "territories" so they can reestablish who goes where, preferably in such a way that they can't see each other as well
2. How much are you feeding? I've heard of some aggression issues when fish aren't getting adequate food so they try to eliminate some competition.
Otherwise I'm not really sure. I've kept black phantoms, black neons, and gold pristellas (8 of the latter in a 10 gal temporarily) and have not had a problem so by no means am I an authority on the subject.
I also have no experience with glo fish in general so I don't know if there are any temperament differences or affects of the different light spectrum.
I'm a little confused since they are same species I wonder why they're behaving that way-unless it is a sex ratio influence as another poster mentioned.
Let us know what you try and if it helps!