ben_danger said:
Surely the whole problem with them trying to turn Luke though CONTRADICTS the rule of the two. Did they organise the whole thing with each other, knowing of an imminent betrayal? (Surely it would have been obvious?)
That's why the Rule of Two is better left out. We can just assume the Sith betray each other because they're heartless bastards who seek power, not because they follow an ancient code.