Exist a option, script or plugin to make this?
Put a different number of renders in one image.
Compositor nodes might do it if no other option exists. Create a scene with render output of dimensions to suit final image size, create another scene and use the compositor renderlayer node to link that big scene in then multiple image nodes one for each individual render and lay the rendered images out in a grid using the mix, transform scale and crop nodes to position the individual images into the big scene canvas.
Hope that makes sense and that theres a python script somewhere you’d be a madman to try the noodle above. 
Or maybe the images to planes addon and arrange the planes in a grid then use an ortho camera and crop after in the compositor nodes if need be.
Why not simply render an animation sequence that matches these poses and then assemble them into your image grid in Gimp or Photoshop? That would take far less time than trying to do it all in Blender.