Do not attack humans
You will encounter your first human in Malchia's domain. He is a vampire hunter garbed in silver armor, shoots silver stakes from a bow, and will be hostile. Leave him alone and continue on to fight the zombie-like vampire. Leave after killing it, and do not go back to the human. The next human you encounter, located in the gear room, should fall to his knees and hold out his arms. The humans now consider you an avenging angel. Do not attack them, or they will turn on you. Warning: Vampire Worshippers are garbed in red and gold. They wield throwing knives and staffs and will always attack. You may kill them as they are evil. Be sure to check your human targets. You will now be able to peacefully roam through the human stronghold.