Teens really need to learn how to do deal with conflict — an important life skill — so let these arguments be their “training ground” for real life relationships. Don’t interfere or meddle. Just be a referee, in the sense that you help them calm down and set ground rules.
For example, if they’re fighting over who gets the car this Saturday, you can help them work out a schedule and brainstorm on ways to avoid this kind of conflict. “What can you do in the future so this doesn’t happen again?”