I was thinking of a device that would make an NPC hostile to everyone on a server except for someone who uses the device on it. So people could have their own personal NPC armies.
There is the “NPC-FOE” SWEP from SG-MOD 0.9 (not the Stargate Pack, this is a different addon)
It makes NPC’s either hate, or love you. Although, it didn’t affect NPC vs. NPC (combine still shoot rebels, but not each other, and vice versa).
Not sure how it works with players around (I haven’t found any servers with SG-MOD. except one roleplay server, but they had it as admin only, and the admin didn’t feel like equipping it).
But still, it would at least stop NPC’s from attacking you. (Good on Player vs. Combine servers…)
or learn expression2, it can do all of that stuff, set relations, move the npcs, even make them talk with lipsync.