Ms. Lyons AP English discussion

I'm curious to know what happened to Ari's brother because I know that he's in prison but no one talks about him the family at all. Ari is not the only boy his parents have but it looks like it is because his parents are acting like his brother never existed or that he's dead. Ari said that in the house there's a picture of every family member but his. and also he dreams about him sometimes.