The images show 3 different aircraft. The first with air intakes on the top, seems to be a "sovietized" YF-23 Black Widow II. The second with
forward-swept wings is a sleeker Sukhoi S-47 Berkut. The third with the airbrake up and intakes under the wing looks like a sovietized F-22 Raptor.
The final one is closest to the actual T-50 airframe as currently proposed.
Stealth in aircraft mainly refers to carbon fiber exteriour skins, with kevlar fuel tanks and fiberglass mixed in. Those particular cloths absorb
radar signals instead of reflecting them. The specific angles also reduce radar signatures and hide heat and light signatures that might be detected.