Why I have this kind of sister?

I’m sad because my family.. Before that my daddy and mummy quarrelling each other .. At that time, I very scare and crying out in room. My brother also crying beside me in my room! At the midnight, they quarrel very loudly sound. But now both of them already nothing and both of them also talking to each other. Happily and laugh out loudly together.
Today, I think no! Because my sister quarrel again with my mother again. This time my sister quarrel with y mother very “big”. This morning she quarrel, she say she don’t want do housework and don’t want to help my mother do any thing. She also say she swear “I’m XXX(my sister) don’t want be XXX(my mother) daughter already.” Them my mum call her go pray in front of God. Then she throw her mop which is he do half way mopping and straight go in front of God and say out loudly. Them run to her room!
I’m very scare, I’m very scare I loss my younger sister… But when they quarreling, I didn’t have any response. I didn’t cry and sad and I didn’t to advise them because I feel this is my sister’s fault. Then my mother punishs my sister with cane. My sister cry and cry. But I also didn’t to stop them!! I sudden felt my self so “cool”!
I don’t know why I became like that. Maybe I agree my mother said that. I’m became a daughter is respect parent and help parent to ligten their load. But my sister didn’t. I scare my sister will became bad and stubborn and not respectfully.
I am scare and sad why I have like that kind of sister. Why?