The judge, Mrs Justice Tipples, told Nottingham Crown Court that the facts of the case were horrific and shocking.
Mr Seesahai was struck with a machete to his back, legs and skull, and was also beaten.
He was killed by a stab wound to the back, inflicted by a machete, which penetrated his lungs and heart.
The fatal wound was 23cm (9.05 inches) deep and almost went through his entire body.
The judge told the boys in their sentencing: “I cannot be sure which one of you stabbed Shawn through the body, only you know that.”
However, she said the pair “acted together to kill him”, adding: “You are both responsible for his death.”
