Here’s how to duplicate the people in your photos for a fun effect, using Photoshop’s Clone Stamp tool
Select the Clone Stamp tool from the Toolbar. You can press the S key for a shortcut to take you straight there. Go to the Options bar and click on the Brush preview thumbnail. Set the tool to a Diameter that’s just larger than the subject you want to clone. Reduce Hardness to 0% for a softer edge.
Keep Opacity set to 100% and tick Aligned. This enables you to paint the cloned subject to any area of the image. Make sure Sample is set to All Layers to account for any new layers. With this set, add a new layer above the Background.
To use the tool to create a clone of the subject, press Alt/Opt and click on the part of the subject you want to clone. Release Alt/Opt and then paint the subject back in to a different area.
Once your subject has been completely cloned to the new position, go to Edit>Transform>Flip Horizontal to mirror the subject. Rotate it slightly for variation using Edit>Free Transform and dragging the corner points around.
To smarten up the edges of the subject, add a layer mask (Layer>Layer Mask>Reveal All). Now use the Brush tool set to black to remove the rough edges and reveal the background around the subject.