If you can create a solid, visual barrier, you can create two separate environments within one cage. I mention that in case you've bought the giant cage already. PM me if you decide to go this route, I have tried it and know some pitfalls to be avoided.
If not, it's just easier on everyone to go with separate caging (and, you probably do have to provide a visual barrier if their cages are close together). Your chameleons will feel safer and so drink and eat more readily if they don't see a competitor nearby. Your life will be easier.
I understand why you might think chameleons of different species can co-exist...particularly since you see it all the time in stores and at shows.