My sister got scared when she saw what was going on in parents' bedroom

Hi, everybody. Today Violet tell her story. But this story isn't really about her. It's about her little sister Helen and how her 'rents' mistake almost led to something terrible.
Our life was quite okay. Well, like everyone else's. My family comes from the South. So, my 'rents had quite a hot liver. Sometimes, they argued. They'd shout at each other. But anyway, it was more or less okay. As girls, we were spoiled by everyone in turn. Mum and dad, and grandma. And our aunt and uncle living next to us. But still, they'd scold me despite I was almost adult - I was 17. And they fussed over my sister.
Helen was the light of our life. No sarcasm. She's really very cool. I'm not jealous for her in any way. 'Cause we have a 12-year age gap. And for me, she's even not a sister. She's my would-be kid. I think I brought her up when the others let me to. But despite we all pamper her, she's a very cool one.
And each time, it only got worse. Helen started to shudder. She was afraid of sharp sounds. And she cried at night... But she didn't even cry when she was a little kid! And then, she became like this. At first, I thought she was being bullied in the kindergarten. Well, kids might be bad. Or maybe, she had a fight with someone, but she didn't tell us? So, I missed my classes one day on purpose. And I went to the kindergarten to ask what was going on.
The teacher said, yeah, they had an aggressive boy. He'd both push and bite someone. But he never laid a finger on Helen. It was she who laid a finger on him when he was too aggressive. And he was afraid of Helen. So, he calmed down at once.
I was happy for my sister. Our dad's the best dad ever. He can’t even say "No" to women. He waited on Helen and me hand and foot. We're only to wile away the time. Toys, sweets, theme parks... Yeah, even if we begged for the moon, he'd do it. He never spoke in a level voice with us. And he didn't punish us or something like that. Yeah, and with mum, he was always a gentleman, always in love. And here, she simply started avoiding him.
We thought some man'd hurt her. 'Cause she avoided her uncle whom she used to adore. But there were no options. She never stayed alone with someone else. Yeah, and she gave the most strange reaction to dad... Mum took her to the psychologist. And she said the girl was undergoing some kind of psychological trauma.
That's where it hit us all. We moved to the frank interrogation. And Helen finally cracked. She said was afraid of daddy 'cause he hurt mum. And so, he'd hurt Helen herself. We all rolled our eyes, seriously. And Helen went on. Dad beat mum and punished her. And mum screamed 'cause it hurt. When we asked when it happened, she shrugged and fell silent.
Everyone just got stunned! Even if a bomb'd fall nearby and we all wouldn't notice it. Well, there was no such thing! Okay, I couldn't know much. Okay, dad's a suspect. But mum'd definitely not forget if dad laid hands on her…
Anyway, somehow Helen said she went for some water to the kitchen at night. And on the way there, she heard some moans from my 'rents' room. Well, and she looked in. And there was dad, punishing mum. On this part of the story, I was just rolling on the floor laughing! Frankly speaking, I don't know how my 'rents explained our little curious kid mum moaned not from pain. I preferred not to listen to this. Not to die from laughter.
But they seemed to convince her. 'Cause Helen stopped being afraid of daddy. And soon, she became herself again. A happy little kid.