Very firstly, you should have to be strong to fight for yourself and your brother. Tell about this harassment to your class teacher and principal. Call your parents and ask for their support, and ask your school authority to provide you and your brother protection from the boy. You should be taken care of by teachers and other staff in the school. 
Ask your parents, teachers, and principal to call the boy’s parents and suspend him for misbehaving with you from the school. 
Do not be afraid of such intimidation or bluster.