I do agree about the stress killing them. And a lot depends on the personality of the two chameleons. Don't you have people that you just can't stand? Same for them. And just like there are social butterflies who enjoy the company of others, there are those who prefer to have their own, quiet space. Do you want roommates in a big place, or be alone in a little place?
I used to have a large free-range set-up. They all had two, 6' ficus for themselves, and at first, I had the new guys isolated from the group. Once they determined that those two ficus were theirs, I slowly started bringing them closer and closer to the "jungle." The jungle was where all of my chams were kept, which included pairs of ficus for each cham. Eventually, their two ficus are brought completely into the jungle. There's about a 3' space between each pair of ficus, so that there's at least some empty, neutral space between the territories. I also had neutral spots to where they could go roam. Most were completely fine, and loved the set-up. I even had two males that would often perch on the same branch together in the neutral zone.
Once in a while, I'd get those chams that just couldn't tolerate it. They would climb down from their ficus and run away on the ground, to an isolated corner of the room. They were never active, always dark in color, and didn't have much of an appetite. The other chams never threatened these guys - just the sight of the others freaked them out. That's when I knew that they weren't suitable for this set-up and had to go. I always had cages set up in an isolated area as temporary housing. I'd keep them there until I could find them a new home. I even had a Nosy Be die in less than 36-hours from stress.