Harry and Neville: Brothers?

[busybuzzbuzz2003]

No: HPFGUIDX 86800

Derek Hiemforth wrote:
> Okay, a bizarre thought just hit me.  With all the emphasis on
> twins in the HP books, and with both Harry and Neville born on
> the same day, is there any chance they are twins, and that fact
> is being hidden from them?
> I've no canon to support this, of course, but it would certainly
> be an interesting twist...


Funny, I was entertaining the Harry/Neville twin idea just 
yesterday! There is certainly something mysterious with Lily, 
Snape, Voldemort. 

What I can't figure out is why , at the end of OoP, JKR threw in the 
possibility that Harry wasn't the "chosen one", but maybe Neville 
was? Was that just fleshing out the story, or is there a lot more to 
that?

Also, the only kids that could see the Thestrals were Harry, 
Neville and Luna. We know Harry saw his parents and Cedric 
being killed, and Luna saw her mother being killed. Who did 
Neville see killed? Aren't both his parents crazy in St. Mungos?