Can I eat humans and sacrifice them to my god?

Solution 1:

Yes, it should be safe to do so under typical circumstances.

To the best of my knowledge, the only thing that matters for cannibalism and sacrifice purposes is whether the creature being eaten/sacrificed is the same race as you; human-type monsters aren't given any special status in those regards if you're not playing as a human. (Human-type monsters are, however, treated as a special case for some other things; for example, genociding a human-type species can affect your alignment record, and killing peacefully-generated humans is always murder.)

Therefore, if you're not human, you should be safe to eat and sacrifice all the fresh human corpses you want, all other race- and alignment-specific caveats notwithstanding.

(It should also be noted that these rules aren't affected by polymorph; what matters is your innate race and not your polymorphed form, so eating a human corpse while playing as a non-human that's currently polymorphed into a human is still OK.)