I need help with null objects.

You have layer 13 as a child of layer 12. Layers 14 and 16 are children of layer 13, so every change you make to layer 12 will also apply to layers 14 and 16. The problem just cascades from there. It looks like every layer is connected directly to layer 12 through the parent tree.

Your naming structure leaves a lot to be desired. The order of when you attach a layer to a parent makes a difference. If you want to keep layer 12's initial scale property from affecting all other layers, you must remove the parenting to other layers before making the scale adjustments. 

I'm unsure why you created this tree full of parent/child links. It looks like you could have just animated the nested comps instead of using the nulls. Try to keep your keyframe structure as simple as possible. Every layer linked in a parent-child tree (some folks call it a chain) will change if you make changes to a parent layer at the top of the tree. Work on your layer naming structure also.

The solution may be as simple as removing the parent link to layer 12, adjusting the scale of layer 12, and then reconnecting the child layers to layer 12.