How to replace placeholder sketches with imported images

I created a complete animatic using Harmony Storyboard Pro with all finished and correctly timed camera movement. The background is made of many plates, which are placed on different places along z-axis, so that parallax movement is achieved through camera motion.
My friend is creating painted background art on clip studio, and the idea was to simply replace the existing layer images with imported bitmap images.
I have been thinking of importing bitmaps into layers, syncing them to parent layer, and then simply hiding the parent layer.
But when I try this, two things happen:

  1. the imported image does not have same scale and coordinates
  2. when the imported image is synced to parent layer, it simply disappears.

Should I be using drawing substitutions instead? It feels like terribly complicated process for simply replacing placeholder art with finished bitmap images. What are your suggestions? Thank you.

Ps. It looks like that in previous version in Harmony, it was possible to export the scene layout to photoshop, along with the camera information, but in version 21, that feature has been removed. I simply can find nothing that would tell me how to paint the backgrounds in external program AFTER the scene layout has been created - it simply does not seem to support that kind of pipeline. Only thing I can think of is to go back to storyboard, replace the plates there, and then export the scenes to harmony again.

One possibility that looks likely is that you are now supposed to export the scene layout from harmony storyboard pro as a pro file to external background artist, and then import the psd with the camera data. Could this be correct?