At a glance, it seems GrublinhurtRight/Left are global or local variables, so when you change them, they will apply to all the sprites. You should make them instance variables of the sprites themselves to make them affect the sprite in question only.
Changing them to instance variables fixed the knockback problem, But they still have a hive mind when it comes to direction. I don't know why the instance variable would work for the knockback but not the direction. Any thoughts?
Thanks for your help.