How to UV Map / Merge the huge City Sample Vehicles Textures?

The Epic Games City Sample Vehicles look nice and are sophisticated setup https://www.unrealengine.com/marketplace/en-US/product/city-sample-vehicles However, the usual way to reduce dimensions with the Merge tool does not yield usable results - actually the merge tool appears to not be able to process VT textures. The vehicles use VT Textures with extreme resolutions and file sizes of ~70MB each.

How can we use the nice vehicles without the excessive file size bloat? I am looking for optimized standard low poly 1024x1024 textures per vehicle. Currently the combined file size when using about 6 vehicles increases my Build by about 3GB, which is about 40 percent of the entire game download size. Without optimized file size I am looking to replace the vehicle materials entirely.

Steps I tried so far:
UE 5.3.2 Merge Tool
Thirdparty tool InstaLOD (Still waiting for the manual account activation after about a week)

Steps not tried yet:
Importing the textures into image editing software and manual resize.
Using Blender and UV mapping manually - generally the textures are UV mapped just the VT textures include dozens of combined textures, and the material instance uses a float coordinate for selection.