ok. when you have your images go to file-scripts-load files into stacks...
this will put all the pictures together.
now to every layer press the icon of mask and give a layer mask to all the layers.
pick a brush and chose the color blackl. and erase the person from every layer.
when you are happy with the result. press ctrl + i and invert the mask. you will see how the person appears again and shows the image of the next layer. do the same with the next layer until you finish showing all the persons you have. its very easy and you can add any amount of layers.