The police execution of an IRA hit
Part of the confusion the boy suffers trying to figure out what really happened to Eddie is that the police killed Eddie in one of the stories he heard, but that doesn't make sense, because Eddie is also alleged to have been killed as an IRA hit for snitching. Ultimately, the boy wonders if the police were executing judgment for the IRA, as if the IRA was the same as the government.
Eddie's innocence
Eddie probably didn't actually inform on anyone. It seems to the boy after his research that actually, McIlhenny ratted, which explains his sudden disappearance to America. Eddie is actually innocent in the first place, in the boy's estimation. (Situational irony).
God and ghosts
In some ways, the boy's rejection of his mother's ghost-centric superstitions is itself ironic, because he is haunted by the death of Eddie, which is a common ghost story trope, and also because as he notices, some of his mother's frantic depression seems like she's being afflicted by a demon. Ultimately, the irony matures until Eddie realizes that regardless of what he decides to believe about God and spirituality, it will be a compromise, since no one can know the truth, and since there are infinite interpretations for every kind of religious experience.
The guilty mother
The mother that the boy loved dearly ends up damaging her son's perception of herself when she succumbs to mental illness, either because she is genuinely sick, or because her religious delusions have begun removing her sanity. In either case, the boy notices that in her mentally disturbed state, she only looks at her husband (the boy's father) with guilt in her eyes. He assumes they don't get along anymore because his mother betrayed them in some way. This is ironic because this realization undermines his expectations about his mother.
Community and independence
The best thing a community can do for itself is to help their young adults to reach full maturity, but in this case, they do exactly the opposite. Instead of empowering the boy, his family and community reject him for his desire to know the truth. Because he feels powerfully connected to his desire for truth, he learns to separate himself from his family and community, feeling lonely, yes, but also individual and autonomous.
