How to apply not moving mask to multiple layers?

I am making clips with moving image on transparent background. Images are RotoTooled before and rendered RGB+Alpha.
My goal is to cut away additional parts of remaining image in several clips at precise position. So far I have been copying the created mask directly to the clip. But I run into problems when I need to adjust the clips size. The mask will change the size as well but this would mess up everything.
I tried to put the mask on Shapes or Adjustment layer and parent it to the clip, but the mask will not cover anything. Obviously I can not mask with Solid due to transparency.
I am sure it is very basic and I am missing something obvious.