I'm going to fight with my partner over my younger sister
What's the problem with your sister?
She burped loudly in the middle of a classical musical concert and she doesn't take care of her partner.
I understand that you're upset with your sister, but what does that have to do with  your partner? It's not right to pick fights with your partner. Why don't you just call your sister out personally instead?
I want to punish everyone for my sister's behavior
I understand your frustration with your sister, but that is between you and her.  There is no need to jeopardize your relationship with your partner over it.