Let's decipher a prophecy, shall we?
"Seven half-bloods shall answer the call.
To storm or fire the world must fall.
An oath to keep with a final breath,
and foes bear arms to the doors of death"
Now the first line...is obvious, the only thing we don't know is who the last demigod is.
The second line: This one is more complicated than the first line, I think storm can be a few different things, it could be Percy or jason for obvious reasons, Khione because she has the ability to create snow storms or it could be Porphyrion because if he is the bane of Zeus/Jupiter, his power could be to create storms as Z/J is the God of the sky, what better ability could you have than to mess up his day and create a big nasty storm.
The 'fire' part could be, in my opinion, Leo because he is a fire user or Frank because of his stick.
And the 'world must fall' part could mean the fabric of civilization will fall, as the gods like to call it, or it could mean Gaia falls.
An oath to keep with a final breath, I have absolutely no idea because there have been so many oaths throughout the two series it could mean anything.
And the last line could mean that the two camps meet on their way to the DoD because it says to the DoD not at the DoD.
Well I think that covers just about everything. cya