User blog comment:It's Good to be the Queen/5 x 12 & 5 x 13 - Dragonlord powers, activate?/@comment-5591912-20121211181102

I think "Brother will slaughter brother" just means that Camelot will be betrayed by one of it's 'brothers' ie. Mordred. And, I think that Mordred and Arthur will both die, and Morgana and Merlin will both live.