what you should try is creating an image in the eimage editor, then goind to the node setup and add it there.
Example for 1 texture:
- Select the diffuse texture
- Plug it into a diffuse node
- plug diffuse node into output
- go to baking tab, select diffuse and only highligth the (color) tab
- hit bake, this will bake the pure color of that texture.
- Save the baked image
now you plug the rougthness texture into the diffuse node and bake again, save the texture under new name. This way you can bake the textures without any shading, AO or other unwanted things. Just pure color
now that you have the textures, you face a different problem, exporting the cycles materials. Sadly this does not work, you need to bake the textures and create a new node setup or use them directly in eg. Unity