How to Create a "REAL" split screen?

Okay so I have 2 images I want to display side by side equally. I know how to do this easily. The issue occurs when I am trying to create a zooming in effect animation for both images at the same time. The image underneath will have no issues zooming in since the upper layer covers everything going on underneath. The issue occurs when I am zooming in (expanding the image size) the image on top. The image on top just starts expanding to fill up the whole space, going past the imaginary line in the middle.

Anyone know how to create a "REAL" split screen where I can pan, zoom, and etc. without either image going over the middle boundary? Here are some screenshots of my attempt.

Created a 3840 x 2160 background so I can place the two images on top. I tried cropping the two images to 1920 x 2160, but it did not work. Once I expanded the images, the resolution just kept increasing.

Split Screen Question.png (447.36 KiB) Viewed 994 times

Why not composite the images together before editing?

Why not composite the images together before editing?

I am new to DaVinci Resolve, so I am not even sure what the difference is between compositing them and simply dragging them in from media pool.

I finally figured out a way guys. I used a mask!

I finally figured out a way guys. I used a mask!

If you have time, please can you explain how you did this?
This sounds like the same thing I'm trying to do.
Three portrait images zooming independently but they are overlapping instead of staying within their boundaries.

Many thanks!