MagiStream

Well, I voted for option 5. While I seem never to finish anything but short stories myself, this sort of problem is exactly why. I lose interest in the book I'm writing because a new set of characters are yammering to be heard.
And while your new story sounds interesting, I think you should try sticking it out on the story you're already working on. It also gives you time to feel out what you want to do with the new one when you get the Chronicles completed. By then you might have an ending you like nailed down that's even more of a twist than what you thought you'd find. Whatever you choose, give your story time to breathe, flesh out and find its Own direction. Outlines and that are nice but make them too rigid or concrete and you leave your story no room to grow organically into whatever monster it feels comfortable being.

[goes back to my & hides again]

Gah, now I've got a new story idea, inspired by John Flanagan's Ranger's Apprentice series. Someone kill me now
Not cool Johnny! Not cool!
But anyway, I think I might just outline The Carrow Chronicles, but not really flesh it out into a story - more just flash fiction (which I won't post, because it'd just ruin the story for anyone who wanted to read the full story).
Then, I'll outline the major points of Andrew's story, while jotting down a few events which I may or may not implement and just write my new idea, inspired by John Flanagan's books.
I just feel, until I've written my new idea, I just won't be as interested in the Carrow Chronicles or Andrew's story (calling it 'Andrew's story' because I haven't got a name for it ).
I'll probably post the book inspired by Ranger's Apprentice MS once I've got at least half of it finished.
By the way, does anyone know if real world settings are included as not my own? Both modern/post-apocolyptic and Ancient Greece (which is the setting of my new idea - I'm calling it Wanderer's Apprentice for now).

Don't worry that your opinions posted here won't matter, I will still write Andrew's story, and I will still write The Carrow Chronicles!
My decision about Andrew's story's ending will be a combination of one of Nerruse's suggestion and option 2, which was the most voted for.
Of course, I'm not going to reveal what will happen - that'd ruin the ending!

Sounds like you really thought this out. I hope you manage to finish it all, it can be tough writing multiple stories at once.

P.S. Can Andrew not be a demi-god? Too reminiscent of Rick Riordan.

Rick Riordan's Percy Jackson myth/urban blend certainly inspired part of this, but there isn't going to be too much of an emphasis on the mythology, just really an explanation for their fighting ability. Otherwise it's just going to look too unbelievable if some ordinary kid who just trains archery leisurely can suddenly fight off mutated animals/people and monsters, if you get what I mean.
Besides, it isn't going to just be Greek gods, I'm blending almost every culture's gods.

I'm not sure I'd read any of those options. But about those gods. Odin was leader of the norse gods. Mars and Ares are the Roman and Greek gods of war. Mars was also an agricultural patron. Mars was second in importance(behind Jupiter). If you want a 'leader' god to 'bless' Andrew don't choose Ares as he was not a really important god being asociated with battle frenzy. If you want a strateic god Athena is a good one to pick. LOL Nerdi correctioning over. They're all good ideas. Sticking through with one though is good, at least until you finish it.