iPhone 5s front camera
Is it possible to replace my iPhone 5s front facing camera with an iPhone 5 or 5c front camera?
No you can't. Only an iPhone 5s camera will work.
NO, it is not possible to fit an iPhone 5 (or 5C) front cam on an iPhone 5S mainly because the proxy and light sensors is differently assembled and attaches differently on the logic board, and sits differently in the body of the iPhone.
No, they aren't compatible. Buy the right part and change it.