It really depends on how large the free range is and the individual animals. We have several forum members with rooms devoted to their chameleons' free ranges, and it works. Not always - you should be fully prepared to separate them at the first signs of stress, but it can be done, depending on the temperments of the individual animals. Now, this means you have to be able to recognize signs of stress - not just the obvious ones, but the subtle signs that you learn only by keeping them over time. If you've never kept chameleons before, don't start out keeping them together. Once you've had plenty of experience, and you know what is normal and healthy, that's the better time to try it. Like sdheli said, you need multiple basking spots, multiple UVB spots, different feeding spots, and lots of visual barriers. It actually works out pretty well with panthers, if done correctly and in a very large area. They are not usually as territorial as veileds - but there are ALWAYS exceptions, and you can't assume that yours won't be those exceptions. Be prepared with extra cages. If you are going to try keeping both sexes together, I would not do more than one male. And having more than one female would put less stress on the girls.
I've seen a lot of members' free ranges with multiple males, and everything works fine with the right conditions and experienced keepers. I'm not sure that I've seen male/female free ranges, so hopefully someone who's tried it will lend some advice.