LW, I'm sorry that your family is having problems at the moment. Its pretty normal & will settle down, hopefully, once the emotions have run down.

If you're concerned, why don't you put your sister to bed & bring your mom a cup of tea? You're old enough now to start seeing your parents as adults w/issues of their own to sort out.

I'd watch out for getting involved, tho. Even your superficial description suggests deeper issues going on than you probably fully realize.