Why, if trying to fake a scene lit by one source, would they even have used multiple lights in the first place?
To provide more light, depending on how much area is to be illuminated.
Why, if these 'double shadows' are caused by multiple light sources, are they only apparent when photographed through a window? This double effect should be seen in plenty of other images as well from the lunar surface if it is caused by something outside the scene and not the window.
Perhaps they used a floodlight for broad illumination and a spotlight to add some density to the LM shadow. You can get a single shadow effect this way however some finer details are lost, the edges are fuzzier and thin spindly objects are somewhat attenuated. Shadows of shorter and less detailed objects like rocks and astronauts simply become fuzzier. Without the extra lighting you might get a result like this, a spotlight effect to the left of the camera
I grew up in an area abundant in sand flats, dunes and beaches. I took standard 8 movies and 35mm silver halide stills around these areas. Never had any effect like this and can't find any Earthly examples except for the oppositional effect that results from when the sun is directly behind the photographer.
And you can continue by answering mine...
Why, if these 'double shadows' are caused by multiple light sources, are they parallel? Shadows caused by multiple light sources diverge and at angle equal to the angle between the light sources at the vertex (source) of the shadow.
If an object is lit by two closely aligned lights then the shadows will remain almost consistent with some slight deviation. Depends on the adjustment of lights and the distance of the lights from the object. If you illuminate a tall object with 2 lights aligned one above the other you'll get little deviation across the horizontal but more on the vertical. Vice versa for 2 lights aligned side by side
When the bush fire season ends in April I'll try to set up some experiments, might have to wait a little longer, just got word, the Corona Virus is in town, they've locked down an international school, just what the doctor ordered!
Maybe I won't have to, looks like others are beginning to pay attention to these curious photos in the archive. Not before time. Thanks