The school will ignor it as long as you let them! Your aunt needs to schedule an immediate appointment with the principal and make sure, face to face, that he is advised of the situation and then she needs to ask him point blank what he intends to do. Make sure she does not go along with her son needing to do something different, i.e., don't go into specific areas of the school in order to avoid the bullies, etc. It is not her son that needs to change anything. It is the bullies who need to change their behavior. It is a well-known FACT that having the victim try to avoid the bully does not work. Nothing the victim does will change the situation. The bullies behavio needs to be changed and that is the ONLY thing that will work!
Then, she needs to go home and write a letter confirming the meeting and what she told him and what he told her. She needs to conclude the letter by saying that they are now on notice of this situation; they are legally obligated to address it; if any further incident occur, she will seek legal advice and if any harm comes to her child, she will sue the school district, and will specifically name the principal in the lawsuit. She needs to cc that letter to the superintendent of the school district.
If she does this, they will KNOW she is serious. Usually the only thing that gets a school district off their butt is the threat of legal action. Oh, and tell her also to go to the police and file a complaint and get some advice from them and then put in the letter that she has contacted law enforcement and then whatever they told/advised her to do.
I am sooooooo very sorry for your cousin. I really hope she is able to get this handled for him!