Character mistake: When Jimmy kills Dave, he says that he killed Just Ray when his wife was pregnant with Brendan, but she was pregnant with Ray Jr (Brendan's brother).
Suggested correction: Jimmy says pregnant wife, little Brendan.
Suggested correction: My father used to tell stories about his nieces and would constantly get their names mixed up. People often get siblings names switched around, and that is when they are in their right mind. Jimmy had been drinking, was still emotional over his daughter, and was telling the story with full intention of murdering Dave within minutes. Fully understandable that he would make this rather common error.
It might be understandable, but not so much within the context of this movie. Would the writer deliberately include in the script that a character will use the wrong name because it does happen sometimes in real life? Maybe if this were a movie about dementia or "Grumpy Old Men", but it doesn't seem to fit in this movie. [I know - not all elderly people have memory problems or lapses.].