My sister told me a few years ago that when she was younger she was abused by our uncle, our mother’s sisters husband for a period of a few months. It happened when she was 12. I believed her immediately not just because she’s my sister, but because when I was younger he made advances at me too but I was older and essentially shoved them off. Nothing has ever been said up to this day because our mum and dad are of wavering health and also Aunt and Uncle live over 4 hours away so we barely ever have to see them. My sister always makes her excuses so never has. I’ve seen him once since sister told me but kept very distant and barely spoke. She doesn’t want to tell our parents and risk making them more poorly so has always kept it to herself. I’ve always respected her decision not to say anything if she didn’t want to but that I’d support her if she did. However, my parents are very close with them. They meet up monthly half way. Chat on the phone all the time, constantly talk about them and my dad considers this my uncle, his brother in law his best friend. The issue is in a few weeks it’s my sisters engagement party, my mum insisted they came and at the time my sister agreed in a panic to keep the peace. Now it’s three weeks away and my sister can’t bear it. She’s having sleepless nights, panic attacks, time off work. It’s worse because this engagement party is happening at her home, so it’s a violation of her space and we can’t believe he’s even agreed to come knowing what he does. We’ve thought of every excuse under the sun of why they couldn’t come, numbers, logistics and each one they’ve come back and counteracted it with a solution. I think she should just tell our parents at this point, but our dad has pancreatic cancer and she’s worried about it “finishing him off”. she genuinely believes it would kill him. She also thought about messaging uncle privately to say you’re a piece of shit you’re not coming to my house don’t come but he’s known to be a violent man in his younger days (prison etc) not sure if he so much is now in his 70’s. Guess looking for any advice really.