AITA for refusing to attend a surprise dinner meant to reconcile my divorced parents?

My parents divorced four years ago and have spoken only when necessary since then. There was no dramatic public scandal. Their marriage had become a long series of quiet resentments, and the divorce made both of them easier to be around.

My younger sister, Erin, hates the separation. She was twenty when it happened but still talks about holidays as if our family is temporarily malfunctioning.

Last month she invited me to dinner for her birthday. The morning of the reservation, she admitted it was not really a birthday dinner. She had invited both of our parents without telling either one the other would be there. Her plan was to seat them across from each other and ask them to “finally clear the air.”

I told her I would not come and that she needed to warn them.

Erin begged me to attend because I am the calm one. She said our parents behave better when both children are present, and she did not expect them to reunite. She wanted one honest conversation so future graduations, weddings and holidays would not require separate plans.

I said using dinner as an ambush made an honest conversation less likely. I also refused to be part of the audience that pressured them to stay at the table.

Erin went ahead without me.

Our mother left within ten minutes. Our father stayed, ordered food with Erin and then called me from the parking lot. He was angry that I knew and had not warned him. I said Erin promised she would tell them after I refused. She says she never made that promise; she said she would “handle it.”

Now both parents feel I protected Erin’s plan by keeping quiet while also abandoning her when it failed. Erin says if I had attended, Mom might not have walked out. She thinks I chose moral distance over helping with a family problem that affects all of us.

She is right that the separate-event system is exhausting. I have complained about it myself. I also understand why she thought a controlled public place was safer than someone’s home.

But I cannot accept that being the calm child makes me responsible for keeping two adults in a conversation they did not choose.

AITA for refusing to attend and for not warning my parents directly?