> Quote - OK, but do you have to start with all of the basic models in the scene and create them together? Do you export them and import them as obj's? Once they're obj's they can't be tweaked with, can they? I guess I'm not seeing how these pose sets are used when the characters are in close proximity.

How many figures you can have in a scene at once, depends more on the specification of your PC, than on your Poser version. Unless your PC is very old, you should be able to load and render at the least four figures, and probably many more on a good machine. To load an additional figure, select it in the Figure library, then click on the double tick (US "check") icon at the bottom of the Figures palette. Be sure to use the Double tick, not the single tick.

Quote - OK, but do you have to start with all of the basic models in the scene and create them together?

I'm not sure what you mean by "create them together". You don't create figures you load them. You can apply a character to a figure by applying morphs to it, or create a character by creating morphs, and applying them to a figure. As to "together", no, you can load them separately.

Quote - Do you export them and import them as obj's?

No, not normally.

Quote - Once they're obj's they can't be tweaked with, can they?

Yes, that's correct. That's one reason why you should not convert them to obj files.

Quote - I guess I'm not seeing how these pose sets are used when the characters are in close proximity.

In Poser, only one figure at a time is the active (selected) figure. When you apply a pose, it will apply to the active figure only. You can see which is the active figure by looking in the drop-down Figures list. The active figure will have a tick next to it (see attached image). To apply a pose to a different figure, change which figure is active (selected).

With pose files for couples, you will have a separate pose file for each figure. There will usually be instructions on how to use the poses in the documentation that came with them. You may need to use 'Set Figure Parent' (in the Figure menu) to parent one figure to the other, so that you can position them both as a unit. You could then translate or rotate  the Body actor of the parent figure, and the child figure would follow.