If you're referring to '.m' files other than those you've created yourself, only the party that created them has the source.
The methods defined in the '.m' files are defined in the publicly available '.h' files which is how we can make use of Apple and third party libraries.
1. The object code created by the compiler is publicly available if free or for a price if not.
2. Would you want to give away the source to your best-selling app?
4. See a copyright lawyer. (However, I think anything one creates is automatically copyrighted as original work).