You would either have to make lots of the same character with different poses and place whichever one you need at the time, or create one character with each pose as a single animation frame, then create a script so you can choose which frame to show.
Either way you would need to do a majority of the work in a modelling program first.
To be honest your best bet is to use software that is designed for scene rendering, things like Daz Studio (that's the only one i know the name of myself, there are more and much better), or you could use a modelling software like blender to create scenes and render the images out from there. That's what those kinds of things are designed for.
You could do it in a game engine, but it would be far more work than using software that is designed for that task, and you would need to use external programs anyway.
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