Datnioides campbelli are the most aggressive of all datnoid species and are very intolerant of each other for the most part.
However, with that said, you can keep them in a group much like you would african cichlids. The key is to give them enough space and hiding places for them to retire when attacked or just to hang out. I currently have a group of 6 in a 60 gallon tank that are in the 1.5 to 3 inch range. I also have a group of 5 in a 300 gallon that are in the 4-5 inch range. And finally I have a group of 6 in a 400 gallon tank that range from 7 to 14 inches. They all get along 98% of the time and the 2% they quarrel only lasts for 2 seconds or so.
Ivan