When adding multiple props to the library, a dialogue box opens that asks you to name your prop. If you click "select subset", you then get the entire list of all the props in the scene in a hierarchy menu. Just click the ones you want to add all together. Then, when you load the prop from the library, you'll load the entire set that you selected. Easy peasy.

If you want to use the duplicate function to duplicate a whole set of props, however, it will only give you the one you have selected. You'll have to do as already suggested -- make a null figure and parent the props to it. Then when you hit duplicate, it will duplicate all the props.

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PoserPro 2014, PS CS5.5 Ext, Nikon D300. Win 8, i7-4770 @ 3.4 GHz, AMD Radeon 8570, 12 GB RAM.