my guards and combat npc's refuse to attack other naturally spawning hostile npc's but the hostile npc's attack mine but for some reason can't do any damage.

You are most likely running a pirated copy of Minecraft. This bug occurs if you’re not using a legal copy with a valid UUID, and therefore we will not fix it. If this is the case, you should close this issue, and I will close it sometime tomorrow if you don’t reply.