Re: Sshaped Landing at top of stairway
The easy way to incur more lateral stiffness is to add one or more intermediate newel posts. The only other way to incur more lateral stiffness is to place the rail system in compression. If the top rail is being pressed toward the floor, it will resist lateral movement. The device to add this compression would typically be sections of steel rod attached to framing at the bottom, and tightened with a nut on top. The nut can be hidden in a plugged hole in the rail. The rod could be hidden inside a bored-out balluster, but drilling through one that's 3 feet long requires special equipment, or a few spares.
Remove not the ancient landmark, which your fathers have set.