2) Yes, a patch turned off the pictures. It fixed many things so the trade off was worth it.

3) There are several unkillable creatures. Ever try to kill a jarl? The collidal warrior is killed by sneaking around and turning a steam switch. Ebora isn't supposed to be killed. But here's a secret if you want them dead. Enter the place and save, immediately reload that save, and all unkillable monsters can now be killed (Dook, Yanmir, Ebora, Collidal Warrior, and others). The unkillable bit gets lost on reload.

4) Yeah, that's a bug. Everytime you talk to the guy who took you through the afterlife, he spawns a set of monsters. The bug is that he keeps spawning them even after you return. But, they are free XP points as far as I'm concerned.