For a 12g tank, I would get dwarf cories. They aren't as common, but other common cories, such as the albino, will get to big to fit a school and have room for something else (as cories should be kept in groups of at least 4, but preferabely more).
As for the other fish, I personally don't like to mix softwater (tetras, rosbaras) with hardwater (endlers) fish, but many people have successful community tanks doing this. 12g is the minimum size tank for the neon tetra, it will still work though. Get 6 or more, don't get less than that. The other fish are also school fish (get 6 or more).
a school of corydoras, a couple endlers, a school of other fish will just about stock the tank.