A quick update to my own post:

I've concluded that the controller unit is definitely faulty and in need of replacing.
I used a multi-meter and measured the resistance from the pins on the connection for the controller unit to each glow plug connector. To my relief they all measured fine.
-After that I lay the problem firmly at the feet of the controller.

Also Ista error codes were showing me that the only good glow plug was cyl.4. If you look at those figures I put down, that makes sense. It's the only one good on both counts.

-Simeon