Didn't read all the posts, but this is my take on the matter, since I lived in a house that was extremely dysfunctional as well.
People tend to get emotional, and it always takes two to start an argument. In many cases it starts with a number of the following
one person inadvertently raising the tone of their voice,
one of them says something and the other individual misunderstands what they're trying to say and raises their voice in response or also in most cases a combination of the above.
This then leads to one or both of them that they are being attacked, and they then go on the defensive, most likely raising their tone of voice again as they get more emotional, neither of them hear how they sound, and automatically assume the other person is the instigator and they are the victim.
Soon neither of them are able to hear what each other is trying to say, and are only hearing certain things that the other is saying, most of it is hurtful in some way or another.
What's happening is an utter breakdown of communication, and the inability to stop and take a deep breath and try to calm down.
What NEEDS to happen is for ALL of you to sit down and explain what is troubling you as their children. But first, they must be willing to listen to each other, this might be able to be achieved by having you stepping into the fray when either of them starts to raise their voice, a tap on the shoulder to remind them to try and stay calm. It helped my parents, though it didn't save their marriage.
Parents don't always see what happens to their children when stuff like this happens. Me and my brother explained to my parents when they came to us and said they were divorcing, that we saw this coming YEARS ago. Even when I was around 6 or 7 years old, though I didn't quite understand it, knew something like this was probably going to happen. A child is much more perceptive that adults think they are.
You guys and gals, need to try and have a long lengthy chat, this is not something that is just between your parents, it involves all of you, and it must be a family effort to try and improve things. Does it suck that the child has to be the first one to take the mature steps here? Yes, but does it have the chance of making things better if the parents realize what's happening to their children because of their constant bickering? Yes it does.
I'm not expert on psychology, but I just felt that I should input my two cents here.
What do you have to lose soap? Actions can make all the difference, and in the end, at least you can take from the experience something that you can learn and grow on.
Sorry you have to live in an environment like that, I wish you luck.