I'm more likely to insist on it if you tell me it's impossible, because regardless of whether or not you can do it, I know I could.

And yes, I would very likely only "mentally" control one character at a time. But the fact is, deciding to use a spell only takes a fraction of the time that casting it uses, so while casting with one I could move or begin casting with the other. Maybe I would never simultaneously decide to turn left on one char, and cast heal on the other, but as my second character is casting heal, and is busy, I can move the first left, a lot faster than if I had to alt tab between them. I can deal with 1/10th of a second delay in "decision" time.

The fact is, it doesn't matter if it's possible or not, because I would need to be able to do it while having access to at least... 40 buttons for each character... That I'm not sure is possible. I don't mind using shift states, but like I said, having my abilities at my finger tips is more important than having a second strafe there.