I do not believe you can complete this easily after you start the racial war.
I completed this by murdering the human guards, then opening the secret door - but the first time I was here there were no guards to murder as I'd spoken to the human leader at the time.
So yeah, I think it's one of those "order matters" and I'm sure the only way to complete it is to murder the human guards up top assuming they haven't already run away (even if the war has begun).
