How to combine textures from deferent objects into one map?

[Mr.Anderson]

I tried to be funny, I sculpted my model and I imported some fancy objects from a free online model. The problem now is that, I have one texture and norms map for the head and multiples materials (with texture and norms maps) for other parts of the model. These imported objects already have their own UV maps and the seams are not marked. I thought I can mark the seams myself and unwrap them into a new textures map and norms map but that went south.
Any solutions? I am so curious to know how to solve this as I can see myself importing and merging models more down the road.

[Dwayne]

You would have to bake them. Note: Baking is only available in cycles render engine. under bake panel of the render tab in properties editor.

1. create a new UV Map and set it active(The camera icon). Then create the new UV map that you want to use.
2. In shader editor, shift+a->inputs->UV Map. Set it to the original UV Map.
3. Connect UV Map node to the vector of your original image.
4. Add a new image node and assign it to the new image. Make sure it is selected. Note:Blender will bake both images. You only need to save the new one.
   For the color use diffuse and uncheck indirect and direct. You will need to do this for each image type. Color, normal, roughness, etc.