Yes, you can kill him (in combat) if you haven't patched your game to 1.3 -- but you don't want to unless you're just looking for a tedious challenge and you have an earlier save so you can do it the right way and progress with the game. You see...Yanmir was bugged. He's not supposed to take damage, but he does under certain circumstances. You're supposed to read the clues and figure out how to make him --- have an accident.
The kids are bugged. I've fixed the script that has them following the player but I haven't figured out what the problem is with the two who won't go through the portal. I'd like to get that side quest working for a later patch. For now just ignore them.
