>>416828627
Try texture baking.
Shitty tutorial made by a nigger: https://www.youtube.com/watch?v=rg3i2YON8tM
Atlasing is essentially just arranging multiple material's UV maps so they all fit on one image and then baking the textures to the new UV map. Cats plugin for blender has a texture combiner that does a similar thing but with varying quality issues. If your UV maps are already packed into squares it's good because it will just arrange the entire textures without touching the UV islands within each UV map. If they have wasted space, try something like UVpackmaster and baking like in the linked tutorial.