Listening verses agreeing

My brother argues and hates my sister for saying she has memories of abuse as a child. He says it ruined our family.
I just listen and say “I am sorry you feel that way but I think we all played a part in our family falling apart.”
I never come out and say I totally agree that I believe my sister, I just say I wish things would have been handled differently.
I see this as lying in order to keep the peace.

However, on a call last week ,Brooke told someone listening to their husband rant about Trump was not agreeing with him and, instead of closing down the conversation, she should say “tell me more.” The caller said she didn’t want to be around that negative energy and Brooke said only her thoughts make negative energy. So should I let my brother talk continue to loop in this unending conversation that gets brought up year after year?

Listening and not forcefully disagreeing has been my way to handle him even though it makes me feel like a liar.

Recently my brother got into a shouting match with my sister when they ran into each other and he said I told him I believed him not my sister. I never said that, I just listened. But he chose to interpret that as I agreed with him. Now my sister is saying she thinks I am dishonest because I am not telling my brother the truth so that means I am probably lying to her too. So to preserve a relationship with my brother all these years, I have now lost a relationship with my sister who says because I was not honest with him it must mean I am not honest with her. I see her point.

So then did I misunderstand what Brooke was saying to the caller? Should I have told my brother not to discuss it with me? Should I have listened but been very clear at the end to let him know I was only listening and not agreeing?