These three threads are full of unsubstantiated stories, changing details and apparent errors.
In all the records I looked at yesterday, and I looked at hundreds, I could find no trace of any Brady twins to fit. Leaving aside, just for a moment, the exact date and place of James Brady's birth (with or without a twin) it would seem likely that he was quite young when his mother died and he might have little contact with his family in later years.