Midgardsormr and the Crystals

[lololink]

The Knowns

It could end up being the case that the Twelve or Hydaelyn were involved

As for what Louisoix gives Alfie and Ali, I'm not sure. He talks about "an ancient art" that lets you summon a primal's power from its defeated essence. I thought he was literally bestowing on them permission to summon the closest thing he could offer to assistance: Phoenix-Egi (because they're Arcanists).

Still spoilers T12 :

The twelves are involved, you see them clearly surrouding Louisoix in the T12 cinematic :
( On the left the T12 scene, on the right the same blades being summoned as the twelve surrouding Bahamut )

Sure the twins might also be able to summon egis but the main thing here is that the primal chose to give their aether, in the case of Louisoix there wasn't much left after he was defeated, but the twelves still had a huge amount of aether, the aether that made Louisoix a primal didn't come from nowhere and you don't see him use his staff to gather the aether and use it on him, he was just waiting his death and then the twelve appeared to him, without any text and just watching the T12 cinematic it's obvious to me that the twelve gave their aether to him. The people were praying the twelves, not Louisoix directly.