I'm afraid it doesn't really work that way. AppleTVs are just there to receive streams from other iOS devices, and access iTunes media from a PC/Mac.
Though, you can stream media from one device to multiple AppleTVs. Just get the Remote app (from the AppStore) for iPhone/iPad and follow the instructions to get it connected to your iTunes library. Here is a screen shot of how it looks from my iPad, which is accessing my PC's iTunes library:
I hope that helps!