1. I'm no mp expert but it may be conflicting with a mod. You may need to activate cheats. Mp runs differently than sp so can't really help here.
2. Damage is hard coded. For mp you'll need to look at the SDK and know either C or C++ not sure which. For sp it is not possible, I think.
3. There is a line in the .npc file that will do that. I only know of it because of the npc tool on jk3files.