All you need to do is to select all of the animating triangles, go to Layer > Precompose - choose to move all attributes to the new comp, name it Triangles comp.
Then, in the Main comp, slect the new "triangles comp" layer and grab the Pen tool. Draw a mask around the Areas you want to be visible (the shape of the inner shield area). This will mask off any areas you don't want.
If you want to animate the whole thing, drag the entire comp into a new comp and animate it. no need to use any motion tracking.
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