It's tricky. I feel for all of you, OP, particularly you, your sister and your mother.
I've got two stories to tell you regarding siblings remembering things differently (and I've got more).
Firstly, my own family. My dad was a brutal, domineering sadist. Like most abusers, he had good qualities. He was a conscientious father in terms of our education, etc. Only two of us remember him as the torturer he was. The others did suffer less at his hands - he had us two to keep him entertained - but have completely dismissed any idea that he was abusive. This is despite the fact that they witnessed his abuse of us and our mother.
A few years after I'd left home, one of my younger sisters phoned me in distress because Dad had sexually molested her. She completely denies this ever happened, but it's burned in my memory. She also denied the long conversations we've had about being scared all the time as children.
I had some long and difficult talks with my mum while I was in therapy. As a result, she arrived a mental compromise where she holds two opposing ideas of her husband: she knows it's true that he abused us and her - she even told me of some memorable beatings he gave me, that I'd forgotten - and, simultaneously, remembers him as a wonderful person worthy of her adoration. Both those things are true, but they were aspects of the same person. I don't know why nobody except my brother and I can cope with this fact.
The second story's about a friend of mine. Her father worked in TV. He and all his media friends had regular family parties, during which the children were made sexually available to the men. Her recall - especially of one of the men, who was cruel - is vivid. As children she and her brothers would talk about it but, on reaching adulthood, her brothers removed all recollection from their minds. They claim she's a liar, personality disordered, etc.
A few of the friends' children remembered these parties and what happened but far more of them have forgotten it all.
Human minds are peculiar things, extremely adaptable. I think it's prudent to remember that different people's minds will try to protect them in different ways.
This is what people mean when they talk about "my truth" and "your truth". It doesn't mean there is no such thing as truth - if facts can be verified, the truth can be uncovered. It's better to say "recollections may vary".
I don't know if, or how much of your sister's story is objectively true, @Cel77, but it's possible you simply have different perspectives on the same facts. Your absence of matching memories doesn't mean she's lying. At the same time, she may be misremembering some things.
Does it matter that much, to you personally, in the here and now? I'd say it's possible to maintain your existing relationship with your parents and repair those with your siblings, while acknowledging what they all say and how important it is to them. I'd say it's possible to say "I see and hear you all, but I take no position."