Keep a line attached to MCs that change scale?

Is there an easy way to have a line attached to 2 MCs and keep it locked to them while at the same time changing the x y and mostly z or scale of those 2 MCs?
I don’t have the slightest clue what to search for here in advance. LineTo?
Here is a simple fle with sort of what I want to do, but I have NO clue how to do it??