Why do my movement orders via trigger get overwritten by AI?

For example Im trying to make a trigger where a Neautral Hostile Unit move/attacks a specific region...
But they always take a few steps and turn around and go back to their initial point all the time.

Neutral controlled units have an (as far as I know) un-overwrite-able AI behavior based on camps. If you tweak the settings in Gameplay Constants related to creeps to max and run a trigger to tell the units to Ignore Guard Position, it should fix your problem. However, no matter what, neutral units will run home if a structure attacks them.

yeah, it also just has to do with how far away or how long the creep is away from it's camp. This absolutely drove me NUTS when i was making my first map.

What you can do is use the "ignore unit's guard postion" found under the AI actions and it won't return home anymore but like Panto mentioned, AI functions do not work for Neutral units so you HAVE to put it on one of the teams as far as I know.

Nope. If you set the Creep values in the Game Constants and make sure that they're never attacked by a structure (set all your structures "Stats - Is a Building" to False), you'll be fine.