Re: unedible and uneatable
I say "inedible" myself. I've never used either of other two.
And I use it to mean that it's too bad to merit being eaten, not that your body simply cannot process it. For that, I'd say "it can't be eaten" not "uneatable."
A rock is something that can't be eaten. (Swallowed, yes, but eaten, no.)
A soup that soup that someone put a cup of salt in instead of a teaspoonful would be inedible.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.