I guess you are talking about the maneuvering with propellers in ports:
The outer Propellers were outward turning, that means while going astern with both engines equally was killing the effect. I'm not aware if a "engine twist" with one engine ahead and one engine working astern was possible. I heard somewhere Olympic could do that but Titanic not. A more experienced person may know more about this point.
The center propeller was right handed and used with higher speeds as I remember, so it was not running while maneuvering.
Other than that I can tell you the basic principle of the propeller walk effect:
When you operate the propeller astern, the water flow is pushed on the side of the ship ahead of the propeller. This water flow is pushing the stern in the other side. For example: starboard propeller astern means flow on starboard side with pressure, the stern is pushed to port and the bow is turning to starboard.
If you can "twist" engines, you could do great maneuvers without tugboats at the stern. But the bow needs at least tugs.
Just imagine you would operate all three propellers backwards: The right handed center and starboard propeller would be slightly stronger than the port propeller and the stern would be pushed to port. You would need to give counter rudder, to hold the stern heading. But this is just theory. Some others may know more about this.
You heard wrong. They both ships worked the same way. The wing props worked independently of each other, and either or both could be reversed at any time. The turbine engine that turned the central propeller was used only when both wing engines were going ahead at 50 rpms or greater. Otherwise, it was stopped. There was no means for the central prop to be reversed.