At one point I had five males together. Two were father/son (but kept separate prior to my adoption) and the other three were unrelated (though two had been previously bonded for ~1yr). They lived fine for a while, then one night one from my original pair attacked the other (one bite, blood shed, from the left hind leg). I separated them based on their activity levels and personality (2+3) and the duo got along great (and still does), and the trio did for a while. One day while I was at work the one that previously attacked its cagemate did the same to one of the others and killed him. Now, I have one pair and two separate. They will turn on each other in a heartbeat. I have only had temporary luck with groups above two, and would not try it again unless it was a family that had always been bonded. Even then, I would be skeptical. I think chinchillas have really good memories, also. One day I took them all out for playtime about 6 months after the initial attacking happened, and the attacker made a B line for his ex-cagemate and probably would have attacked him again if I hadn't intercepted.