Continuity mistake: A few brown smudges appear on Alice's note, written on a torn page from The Merchant of Venice, after Bella finds the book. (01:00:20)
Continuity mistake: Edward is about to walk towards Aro. As Renesmee looks up at her father, a substantial amount of hair is covering a quarter of forehead. In the next shot as she's moving behind her mother, her hair is now neatly parted, and her forehead is no longer covered. (01:15:25)
Continuity mistake: At the end, when Bella is thrown into Edward, she is wearing shoes with a heel, but a few seconds later she is wearing regular boots. (01:32:50)
Continuity mistake: During the confrontation, Aro asks to meet Renesmee who proceeds to touch his face with her right hand. From her perspective, the fingers are well below Aro's side burn. From the opposite shot, her fingers touch his hair.
Continuity mistake: Bella has green eyes in the hospital scene in Twilight (close up shots) but when they zoom out she has brown eyes again.
Answer: Aro also makes the argument that for the first time in our history humans pose a threat to our kind with their weapons that can destroy us. Theoretically any weapons that can tear apart and/or burn the vampires would work. So, yes, things other than vampires and werewolves can kill the vampires and werewolves.