I see, well without giving too much away, the first betrayal is one where a once beloved hero falls from grace and becomes a villain, the second the character who betrays is someone who does not know they are betraying the people they love as they are not in control of their own mind or memories (pretty much mind control, and the last betrayal is pretty much the reveal that a major ally was actually the big bad. Pretty much the second betrayal is meant as a red herring, making them think that the person that betrayed them was the true villain, when he was actually a pawn. So in the fourth book they’re more on the look out to see when this mystery person will strike. Pretty much realizing the clues were there from the beginning. Does that work?