Hey, when importing to Unreal - the materials are likely creating a standard material with a single image map connected in the shader graph.
For each object/asset - if you double click on the material slots as there are multiple slots per item(this is where it becomes a bit time-consuming):
1. Use the editor button to find the linked material.
2. Double-click that material in the content editor to open the material shader graph.
3. Manually set up each material to use the corresponding texture maps.
4. Connect any relevant texture maps to the required output nodes on the material shader.
I am replying from memory and it has been a while since I used these assets, but if that does not help please post again or contact me on discord and I will see if I can help you further.