I would say guilt trip them...but god, don't do it. How old are you, if I may? I assume your parents aren't normally violent people/heavy drinkers?
You can try talking to them...maybe even suggest counselling? If you have a sit down with them, let them talk it out with each other, add your opinion or thoughts where necessary (mediate if you have to). If all works well, they'll realise that they've made a huge mistake, give you a huge hug and bake cookies.
But seriously, the last thing they want is to see you unhappy, I'm sure. You have to tell them what they're doing is upsetting, and you don't want to see them resorting to physical violence to get their message across. That's all I can really say...that and good luck, and I hope everything turns out for the best. Stay strong.