I'm also a big fan of Red Terrors, and kept a group of 6 in an aggressive community tank for two years. Started with juveniles in a 65 gal
. Then expanded to a 120 gal
. I found that out of the group, only one male and one female actually colored up. Both quickly outgrew the others.
I kept a beautiful male RIvulatus, GT, with the RT's. He was larger, and more aggressive. The GT's bad attitude actually kept peace amongst the Red Terrors. They evidently were too worried about the GT to fight each other.
You don't necessarily have to make a wet pet out of Red Terrors if you have a big tank. Don't believe everything you read about their potential huge size and uncontrollable aggression.
My largest male and female only reached approx. 9" inches. Tankmates included Silver Dollars, Plecos and various Mbuna used as Dithers. The Mbuna were a big mistake, and I rehomed them. I lost all my Festae to an Oodinium outbreak, introduced into the tank by a quarantined Texas Cichlid. Since then I've gone another direction, keeping Red Texas, Firemouths, and a very docile Flowerhorn.
Might consider adding a few larger, juvenile Firemouths to your tank to help dilute the baby Festae aggression. The Firemouths can take aggression and also dish it out without harming anything. Introduce some BN Plecos and maybe some Synodontis catfish or tough Botia Loaches like the Red Tail or Tiger. No Cory cats. They would eventually be eaten. Be sure to hardscape your tank to break up the line of sight and allowing for numerous hiding places.