How to not have two layers opacities adding up?

Hi all! It's pretty obvious that if for example, I have one layer with an image of two people, and a layer underneath with a house, so the two people are standing in front of the house, and I want to fade this image away, if I decrease opacity from 100 to 0%, when it's i.e. 50%, you see 50% through the people and you see the house too.

Now if I want to have both objects fade away from 100% I can nest them, and have them fade together, so at 50%, you see 50% of the background, and you never see the image of the house through the image of the persons. 

Sometimes in my projects, it's very impractical to create a pre-comp just for this. For most other aspects I would use a null object, but since null objects already are transparent this doesn't work.

Is there any other way to have two images fade together instead of separately into each other? I'm just curious. Keen to hear!