Jenova aint making Sephiroth beleive he is a Cetra and he aint beleiving he is one either. Where you get that idea ?


Aeris: Sephiroth is different. He's not an Ancient.

Cloud: He shouldn't be able to find the Promised Land.

Sephiroth: ...Ah, but I have. I'm far superior to the Ancients. I
became a traveler of the Lifestream and gained the knowledge and wisdom of the Ancients. And soon, I will create the future.

Jenova aint making any one beleiving anything it s just like any puppet working for Sephiroth it is one of the reason why you fight Jenova Before sephiroth too. Everything i posted show that Jenova have no control over Sephiroth. Else Jenova would have wanted to be protected by Sephiroth but he was the one controlling the other and this is why you get to fight Jenova before him.