If the parents of these boys are allowing them to act out in such aggressive and criminal ways, they are not doing their job. I'd speak with our attorney about filing civil charges against the parents on behalf of their abusive children. You can also file a restraining order against these children. If they try to harm or intimidate your DS, their parents will be financially responsible. Maybe that's the wake-up call that they need to learn some parenting skills. The threat of civil action may cause them to take action to try to reform their children.
OK, for those who will say that you can raise two children in the same house, the same way and have one turn out to be a brain surgeon and the other become a bum, I agree. However, a meeting that was attempted with one of the parents proved to be futile. If the parents are in denial that anything is wrong with their DS's behavior, you'll get nowhere fast. Yes, someone has to be held accountable.... it should be the parents of the rebels.
As for the school not taking this situation seriously, you have the option of taking the situation to the media. A school that is run by it's secretary is not being run properly. (Not that in many situations the secretary doesn't actually guide how the office, organization, shool is run.) The secretary alone can't possibly do her job and be expected to be the asst. and principal at the same time while the Asst. Princ. is in class. When I'm not at work, my network administrator is authorized to act upon my behalf.... that goes for staff issues, equipment and software issues and interdepartmental issues. My job is always covered. The school leadership responsibilities are even more important, IMHO, than making sure a system is functioning 24X7. We have contingencies in place for equipment failures. It doesn't sound like the same is true even though the school is dealing with human problems.
My prayers are definitely with you and your family. Please keep us posted.