Unwrapping Multiple Objects to One UV Map

Trying to unwrap multiple objects in blender with the texture atlas add on. Kinda figured that out, but when we tried to export it as a UV map, it was blank. Is there something we’re missing here? Is there a way to unwrap multiple objects to one UV map? Our guess is the texture atlas is NOT a uv map, its just a texture, but we need it to be one UV map. Is the only option to join them, unwrap that, export THAT uv map, then unjoin it and use that as our models with the joined uv map? Or do we have to use the show other objects setting in the uv map, then export that as our UV map for multiple objects?