i see how that works. however Jenova wanted to (SPOILER)destroy the world while sephiroth wanted
(SPOILER)to become a god and rule the world

So i believe Sephiroth was strong enough (SPOILER)to break free of his jenova cells commands and manipulate jenovs own manipulation 2 get in an advantagerous position

and remember
(SPOILER)Sephiroth was injected with jenova cells in the womb. it was part of his genetic makeup. in essence sephiroth and Jenova had become the same entity