Even if they did kill the author the original book has already done it's damage, and how would they know she's writing another book? If they did kill her they could write their own book to make them look good if they can copy her writing style.
@kiwicakeu Reread the first chapter, remember that the twin grew up with fear and disdain. So he grew up like he is now, but all of sudden apparently people like him now. Of course he wouldn't like it.