Woah, that's quite some story. O_o
I totally agree with your sister kicking her ex's asses when they acted like idiots. But you're right, there are some things (like death) that people don't deserve for just being douches.
I know how it is to have a dysfunctional family myself. My parents and my sister are the only ones I care about. As good as all of my uncles, aunts, cousins and even my grandparents (the ones that are still alive) are actually assholes. Some of them are just jealous that we had pretty much the hardest time in life and yet we managed to do so well while others are simply selfish. i.e. My aunt that is so pissed and jealous that I had better grades in 7th and 8th grade than her daughter, my cousin, that she went to the teachers and made a scene how it was possible that "I could be better than her daughter". Seriously. Now she is pretty much forcing her to go to college so she can just be "as good as I am". I'm not even sure she finished the first year while I'm about to finish my fourth year in college. How come I don't know? I don't ask, I don't care.
I don't "hate" them, I just want them to laeve me alone and never contact me for the rest of my life. I got a new cellphone number especially for that and nobody of them has my number.
There wasn't as much violence in my family, but regardless it's fucked up. That's mostly because of disappointment in how weak family bonds can be and how they can be like that towards their own family.