Ok this is something interesting. A short time after I read this story of yours I was reading my bible. I happened apon the story of Ishmael and Isaac's births. There's a bit of an eery comparison between your story and the bible. The one major point was that when Isaac was born he was blessed greatly by God where as Ishmael wasn't. I found it interesting that in your story it turns out that Ishmael is "cursed" you could say and Isaac isn't. Just an interesting thing I stumbled apon and was wondering if you did it on purpose.
Author's response
Thanks, but I think you're giving me way too much credit on this aspect. I was only thinking that the characters were twins and needed names that started with the same letter, then picked two random names from the Bible. It's an eerie coincidence, though, but it wasn't on purpose. :)