Each client is running in its own folder.

It's hard to tell what is causing the blue screen. It could even be possible that it's something related to autohotkey. I just remembered that when I first set up ingame macros, both toons were sitting in town for quite a long time without any problem.

It's when I run away from town and start questing that eventually I crashed.

I can't do any testing tonight because my computer is chugging on something in the background that I can't afford to lose. Tomorrow, I'll see what does happen if I run 1 fullscreen and have another instance running.