She won't see any wrong in your Dsis, because she is cut from the same cloth.
They are not 'in the wrong' as they see it, as there are more than one of them all the same, it makes them think they are right. My Mum and Sis are the same. Deluded.
we go through all the turmoil of life with these people, never feeling good enough, depression, dysfunctional relationships etc because we are trying to be people like them, to fit in when we simply can't. We are caring, compassionate, generous, love people, love life. They are NOT.
These people will deny, deny and deny until they are blue in the face, they think that you have no right to question them, that their behaviour was fine, totally unremarkable, but that is because they are ALL deeply flawed beings.
You all know the truth now, your DC support your decision, move ahead all of you and put these terrible people behind you. At least you do have solidarity from your XH, that really helps.
You know you said what you needed to say, you know it was valid and that it was checked by others that were present/involved in the events at the time.