I want to show two different 3d objects in my plot. I want the first to be on top of the other.

For that I need to control their position in the 3d space, AND to control their apparent size.

I am not uploading the stl files I am working with because of license considerations, so let's have a look at two files from the wolfram examples repository:

Show[{Import["ExampleData/seashell.stl", "Graphics3D"],
  Import["ExampleData/spikey.stl", "Graphics3D"]
  }, PlotRange -> All]

This effectively plots only the spike. I guess because the seashell is inside it.

How can I translate one of them by some vector {x,y,z} and how can I resize one of them by some factor m?

Moreover, how can I orient it so that it "points up" in an arbitrary direction {u,v,w}?

Thanks a lot for you help.