What would I have to do to take such photos from a 50mm lens of a Dx camera?
You can't take those pictures with a 50mm lens and a DX (1.5X APS-C) camera.
To fit all of what an 11mm lens will give you you'd have to back up five times as far. But that would change the perspective, or distance relationships between the various parts of the scene. To get those photos you must have the camera in the same position and a lens than can shoot that wide. There's no other way to do it in a single shot.
The closest alternative using a 50mm lens would be to put the camera on a panoramic head that rotates the camera around the optical center of the lens, take a grid of overlapping frames (going both left to right and up to down) until all of the scene is included and then stitch them together after the fact.
The only thing you can replicate more or less exactly with the same camera and a different focal length lens by changing your shooting distance is a perfectly flat target that is perpendicular to the optical axis of the lens. For everything else, the change in perspective will change the way the various parts of the scene look compared to the other parts of the scene.