If I understand it correctly you want to merge the independent objects into one. Poser was never designed to do such operations. It was, and rightly so, considered that 3D programs like Blender are better suited for the task. Problem with those however is they come with a steep investment, if not financial then in learning effort. 

A quick route to merge props without resorting to 3D programs is to export your separate props to a .obj file. On reload you willt have all selected components in a single prop.

in a new scene.