Hello and welcome to PSG.
Unfortunately, inquires such as this often go unanswered. There's simply far too much going on to be able to say for sure what techniques were actually used much less give you a step by step instruction. Any guess on our part would be purely speculation. Photoshop literally has hundreds of thousands (if not millions) of possible ways to edit images.
I do know, based on some digging, that these images were photographed by a German photographer named Norbert Schoerner in 1999 for Prada. I suspect Photoshop was more than likely the culprit. The subjects were isolated from their original backgrounds and composited into the backgrounds you see above in your examples. The new backgrounds appear to be illustrations, but unknown as to what program was used to create them, Photoshop, Illustrator, or AutoCad maybe? While I don't think so, they could have possibly been generated in a 3D program. Not sure what 3D was around in 99' so it's hard to say.
There's definitely some skin work (smoothing) added, more than likely
Frequency Separation that was popular back then. However, there are now many different techniques that are used nowadays for
skin smoothing.............it would just be a matter of choosing which one suites your taste.
The clothing, other than the girls shorts, appears un-edited and only enhanced. It would be a coin toss guessing what technique was used. It's hard to differentiate what can be attributed to photography, lighting, and post. The subjects are both brightly backlit. There also seems to be some selective "outer glow" on the male subject. This can be achieved through many different methods.
Perhaps a better approach for you would be to narrow down your inquiry to something a bit more specific rather than asking about the entire image.
Let us know!
