Need to combine Pyramids into a Cube

Hi all,
I am working on a project for class and ran into an issue at the end. I have 6 pyramids stored in separate stl files that need to be scaled down and made into one single cube that would then be printed.
I attached each of the 3 stl files containing a the pyramids below. Each pyramid is used twice for the sides of the cube in the name of the file.
Any help on this would be very much appreciated
It is also worth nothing that for this to work each pyramid has to be scaled such that the height is half the length of one of the edges of the square bottom.

Sorry to inform you that your model elements are not 3D print compatible, you have 2d faces that are infinitely thin, triangles that also taper to infinity by meeting at a single vertex. I might be able to shell it for you but it will need to be quite large and thus expensive to print. I'm trying a volumetric retopo as I write this. I'll be back -S

EDIT: New info, your model also suffered from random flipped normals prompting the comments above. Simple shelling has restored the model to what I think you intend, 1, 9 and whatever number of windows on each opposing face tapering to the middle. I'll see if it passes the model checks. -S

UPDATE: Ok so your Menger sponge failed one upload/technique and passed a preliminary test after a volumetric retopo and some clipping (zbrush terms). The model is NOT error free due to the assets and information supplied (or not). If you want a clean version PM me or wait for the other freelancers to PM you. The model does not have to be as big and expensive, I just chose this material and scale at random. -S

Repaired and fixed in Netfabb and DesignSpark Mechanical.
Nice model.
https://www.shapeways.com/model/3dtools/4595844/0/6?key=bf0b a48018d632cab7590c6f2ddfc178
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