What you should have done is called the police, gone outside if you felt you could safely get the people out of the car. Get a description of the scumbags and write it down. Get a license plate number and description and write it down. Let the police do their job, it is not yours to do. Your actions came out lucky this time. If you take matters into your own hands, be prepared for any and all consequences.

You are worried about how the family would react to you beating him up? Imagine how the family would react if he would have died in a car accident due to you chasing him. Play it smart dude, I know you are a smarter person than what I have read above.