Kaodi, Sachiko has been raised as a human...she doesn't know herself. She knows she's not like other people, but doesn't really understand why.
I suspect Angry Elf's parents probably knew (because they most likely saw her mother die), but they didn't really understand what they knew (never having seen the foxpeople before), and hadn't decided how to bring it up before the tragedy struck. I can see elves taking a few years to work that kind of thing out...always thinking it'll be easier when she gets a little older, until oops! Too late.
You can decide if Angry Elf knew, and what he knew, as you see fit.