For some reason I was assuming Reaper's Cove was the whole area, you're probably right there.
Although, this list you posted is full of achievements that do not exist, I'm only mising 5 and I know for a fact that Sebille and Beast have 2 achievements each so there's only 1 remaining achievement slot, which can be one of several in there (Deicide, Lawyer up and Isle of Last Resort are the ones I can think of right now, I think only Isle of Last Resort exists among those).
As for your other question, these are the achievements I'm currently not able to get: Sebille and Beast's quest achievements (both for both characters) and Isle of Last Resort.
http://larian.com/forums/ubbthreads.php?ubb=showflat&Number=629043#Post629043I posted it in "Technical Problems" subforum, no response yet.
Edit: Got Isle of last resort, the other achievements I mentioned do not exist (on Steam at least).