Before you can identify the causes of the main conflict in Miracle’s Boys, you should probably establish the main conflict of the story. It seems safe to say that the main conflict involves Newcharlie and his contentious relationship with his younger and older brother.
One cause of their conflict might be Rahway Home for Boys. This is the juvenile facility that Charlie is placed in after he holds up a candy store. The juvenile facility is what turns Charlie into Newcharlie. After Charlie gets out, he’s transformed into Newcharlie: he’s withdrawn and irascible. You could argue that the traits instilled in him at Rahway Home for Boys are a notable cause of the conflict.
You might also identify Aaron as a vital cause of the conflict. It seems like Aaron encourages Newcharlie’s bellicose posture and, in doing, exacerbates the central conflict between him and his brothers. Aaron and Newcharlie seem to have a relationship based on mutual idolization. According to Lafayette, Aaron would kiss Newcharlie’s shoes. Meanwhile, Newcharlie is “just as stupid over Aaron.” It seems reasonable to suggest that without this toxic relationship, the central conflict between the brothers would be less keen.
Finally, you might cite the death of the mom as a key cause of the main conflict. You might speculate that if the mom was alive, there’d be less pressure on Ty’ree and less conflict between the brothers. Although, you should probably note that Charlie was not exactly well-behaved when his mom was alive.