So, I am trying to make sense of the ending of Dream Drop Distance. Master Xehanort wants to pit seven lights against 13 of darkness in order to recreate the x-blade. Now, in the final scene, Yen Sid says

 

"Thus, even if we deliberately avoid finding our seven lights to avert another Keyblade War, Xehanort will still target the seven princesses in order to forge the x-blade."

 

Ok, but then he says,

 

"To protect the seven pure hearts, we will need seven lights strong enough to stand against the thirteen darknesses."

 

So, to avoid putting up seven lights to complete Master Xehanort's plan, they're going to get seven lights to defend the princesses? That kinda sounds like they WANT to follow through with his plan. Why seven? Seriously, you could've gotten any other number of lights to protect the princesses and you would be avoiding forging the x-blade. Heck, now that Kairi is a gonna be a fighter, you only need six. It seems like they're setting themselves up to fail. Am I missing something? And if the Princesses of Heart were the seven fragments of light from the Keyblade War, what became of the 13 darknesses?

They really don't want to follow Xehanort's plan, but if they don't put up any defense, Xehanort will target the Princesses to forge the X-blade. I'm assuming that they're going to gather MORE than seven people to fight 13 beings of darkness, but among that army will be 7 chosen guardians of light, and when they clash with the 13 darknesses, the X-blade will be forged. Either way, the Keyblade War is inevitable, the X-blade will more than likely be forged, but the what they're trying to avoid is total destruction of all the worlds.

Xehanort spent a long time coming up with this plan- whether they act or not he's going to get what he wants to happen no matter what, it's just up to the heroes to put a stop to it after it happens

Kairi is going to protect herself and the other princesses

Well , forging the X-Blade and provoking the Keyblade War are both inevitable . The seven fighters ,though , are going to do their best to protect the worlds and the seven Princesses ,even if they have to fight the 13 Darknesses and start the Keyblade War .

That's how Xehanort is forcing the clash to happen by ensuring that either way the 13 darknesses vs 7 lights will fight. However if the PoH are worth more then the Guardians of Light (as they literally make up all the light in world) which group would you send out to fight?