Look, you should give them a lecturing but even so, don't expel or punish them severely. They were RAPING a person. They were also about to take a picture of somebody they were RAPING. These guys hit them to stop that.
Also, I think his parents have the right mindset even though it's sudden. There, most of the students are going to give him a hard time. Somewhere fresh will make it easier for him to adapt to his situation, even though it isn't something he likes. But if you're going to do that, he needs therapy and a better support system.