There are three priorities in the case of a car accident, and if you keep them in order this bad situation can move forward as swiftly and simply as possible.
Don’t leave, make sure all of the passengers and drivers are awake, conscious, and not seriously injured. Even if it was the other guy’s fault, if you are worrying about your paint job while his wife has serious injuries, things are going to go poorly for you in the court of public opinion. In this day and age, even if you don’t feel ethically compelled to be kind, you don’t want to end up as THAT guy on YouTube.
Call the Right People.
You should make two phone calls immediately, the police and your insurance. You may want an attorney, but this is not a call you would make immediately. The police and the insurance company will be the ones to handle the immediate aftermath. Do not talk about the incident with anyone but your insurer and the police at the scene. Do not speak with the other driver’s insurer, they should only contact you via your insurer or attorney.
Take pictures, get a copy of the police report, ask questions of the people who witnessed the accident. You want all of the information to be gathered, but not clouded by early legal posturing. You cannot have too much information, and if a lawsuit comes about, this documentation can make all the difference.