Same species only though. And don't put more than one male in an enclosure. Make sure you have plenty of room that every pygmy can be alone and hide if they feel the need to. You have to keep a close eye on any signs of aggression, but that's usually not a problem.
I assume that this will be you first pygmy chameleons...
If Yes, I recommend you to start with Rieppeleon brevicaudatus.
They are cheap and the best pygmy to start with(my oppinion), because you can keep them almost in any enclousure and they are easy to keep and breed.
Other species such as Rhampholeon spinosus or acuminatus are more difficult to keep and breed, because they need a good night drop and you must also watch the daily temperature, the daily temperature by this species may not exceed the 22°C(my oppinion and experiences).
Pygmies seem to do well in groups; if possible, you might try for one male, two females (so one female is not left being the sole center of the males amorous attention). If you do a search on some of Brad Ramsey's posts (like this one), he's recently put in a lot of observations about group behavior in bearded pygmies.