[color:"orange"]Since the King doesn't key on you until you're pretty close (and doesn't move randomly), should be easy to clear the cave all except for him.[/color]
I loaded one of my old saves to double check, and only the troll king should be visible when you first enter the cave. Once you near the section of the cave he is in (ie get within about 3 times the character height from him), the cutscene conversation is triggered. When that ends, the king turns hostile and the other trolls fade into existence at several places around the cave.
It seems that your game is placing the regular trolls there too early, which may or may not be part of the problem with the game crashing. You could try running past the trolls and not attacking any until after the conversation with the king.
[color:"orange"]You say they "restarted the game" - does that mean they started a new game, or just reloaded?[/color]
They started a new game:
Constant desktop crash.
Your save appears to work fine on my system, and I was able to clear out the troll cave and do some other running around without any crashing. The problem may be something in the game files, or a conflict with something in your system. Try the file verification method in the topic;
Troubleshooting Tips (& manual install procedure)