I have created and earth with clouds from 2 spheres one inside the other inside poser. I'm trying to figure out how to create a single object or prop out of the two of them together as one.. How can I do this?

File>export>wavefront obj check both spheres and nothing else. Then file>import> wavefront obj. uncheck centered in the pop up window and leave everything else the same. You'll have one prop. You'll probably need to reapply the textures. Only the very basics with save in an obj.

Or just save them down as a combined Prop to the library. Parent one sphere to the other first.