Hmmmmmmmmmmm. Let me analyze this. Your brother did one thing right and everything else wrong. The seatbelts saved the day, and his mistakes were probably due to inexperience.

I think it was a little wet on the roads,
(An experienced driver becomes very cautious when roads are wet.)

but on the way back 2 of my other friends were in the back seat arguing. Well my brother turns around and tells them to shut up.
(He allowed his attention to be distracted from his driving. He should have stopped before telling them to shut up.)

By the time he turned back around he was a little bit off the road but heading into a curve. Instinctively, he jurks the wheel back toward the road.
(Overcorrection is a major cause of accidents when inexperienced drivers are involved.)

He then sees a car comming and panics causing him to jerk the car back the other way.
(He overcorrected again.)

I also found the policeman's comments interesting. As a young reporter on a small daily paper, I used to cover a lot of accidents. I remember a fatal accident that happened at less than 30 mph and the car had only a dented fender. Unfortunately, the driver's door popped open and her head it the pavement. There were no seat belts in those days.

More recently, a friend of mine and his mother both died when they were thrown out the driver's door. They had been sitting on their seat belts, when they made a U-turn and got hit just behind the post between the left side doors.

With seat belts, they would have survived. He was my barber, and an antique dealer. I used to get a lesson about antiques with every haircut. I miss him.

I'm glad everybody was OK in your accident. Think of it as a learning experience.
Howard