There was a similar question the other day - maybe some of those answers will help you too: http://www.mamapedia.com/questions/16504437585729617921
It seems to me that they don't have severe enough consequences. I think you do not have to intervene all the time - just separate them and tell them the consequences will be severe and immediate if a) they touch each other, b) destroy anything or c) talk loud enough for you to overhear it.
Arguing over the TV? Unplug it or - no kidding - put it in the closet (Yes I know that impacts you too but sometimes you have to be drastic). Arguing over the dishwasher or the table setting? Stop cooking for them. Not one meal. There are no dishes? Oh well - just take out what you need for yourself personally. Really. They will not starve without a vegetable or a real meal for a few days. They can live on PB&J they make themselves 3 times a day - that will get old really fast. Privileges or day trips or treats? No, sorry, they are too immature - they not only fight, they blame the other one. Do not do their laundry - after all, you are too tired from unloading the few dishes you yourself need or setting/clearing the table. They will not die from having to wear their clothes again, but they will be humiliated. That's okay. You are simply not interested in doing one single thing for people who are so unappreciative and so disrespectful of family and caring gestures. The point is, you take away EVERYTHING that is the subject of an argument or disrespect. If the family room and their own rooms are bare - terrific! Very graphic! Everything in their house is a privilege, not a right, except for extremely basic food and a roof over their heads and a bathroom.
If they are so incredibly angry that they need counseling, then set that up. Maybe a few sessions in how to negotiate and appreciate would be good - perhaps instead of summer camp or time with friends.
Don't argue, don't referee, don't get involved at all. This will take all your patience and resolve.
They are at the age when they want more independence. Take that away. No, they are no going anywhere because they cannot be trusted to watch their mouths with others or be respectful of other people. If they say, "No, we can control it elsewhere" then you of course say, "So, it's a choice to act the way you do at home, because you actually know better and can control it?" Then you are too immature to be worth my time. Be ruthless. It will work. My guess is that they will not do this in front of Grandma. But if they do, don't tolerate it - they can sit outside 100 yards apart at her house too - just far enough to not be able to hear each other's BS. If anyone asks what they are doing there (neighbor, police officer), they can just explain that they are too young to behave themselves and they are in time out.
Do not let them run the show. Take away anything and everything that is important - no threats, no warnings, just do it. Refuse to argue about it. This is excellent practice for the teen years!