I have only gone through IV once (Translated SNES ROM) ^.^

Interesting question, but I think it was Goblez controlling Kain while being controlled by Zemus. Chain mind control with Zemus being at the root of it.
- This

And yeah, Edea was Completely Void from any Pain she caused throughout FFVIII, but when she "Snaps" out of it, She completely understands that she may come possessed again, and become a being (Mentally) with a completely different set of Morals, with no reachable willpower/motives from the real "Edea".

In IV There are moments when Kain and Goblez Show that unlike Edea they still have Scraps of Willpower, Goblez refuses to Kill Cecil at his highest chance of doing so due to Brotherly Love, and Kain, Like Goblez, Has a hidden weakness, Rosa, which is abused by Zemus - Goblez - Kain Mind Control.

But I'm no expert when it comes to IV, It's one of my many Favorites, even if I have only palyed it once, I thought the mind control was pretty straightforward, but I have not played FFIVTAY, so maybe I'm missing out on some other Information.