Open all the images
Drag all the images onto image you've set as the base
Using layer masks, erase all the areas you dont want on each layer, leaving the base layer left alone
Using the above techniques in a similar fashion, you can do it by...
Opening image
Duplicate base layer
Apply a saturation adjustment layer to the base layer, desaturating it completely
Make sure the adjustment layer is between the two layers too, or it will desaturate both layers
Using a mask on the top layer, erase all sections you dont want.
EDIT: Sorry if that's a bit complicated for you guys, that's the way I do it as it's completely non destructive, meaning you can always erase the masks or the adjustment layer to go back to the original document.