"Where in the Foxtrot Feather step does the most sway take place"
In ballroom terminology sway is a position, not an action. As a result it doesn't really take place.
What happens is that you swing (an action) and as a result of the combination of upswing a side lead (usually developed through CBM) you end up with sidesway.
You would probably have the most sway as you are arriving onto step 2, as you come fully over it your body will reorient perpendicular to the floor.
It's important that the swing that creates sway against the travel result from the hips moving faster than the upper body, not from the head or shoulders moving backwards - you can't swing while staying in one place on the floor, so you shouldn't try to achieve sway without moving either.
Also note that we generally avoid swaying into the direction of motion, as this would drive our partner into the floor. The small exception occurs in a few steps - tipsy for example, where they head weight briefly hints in that direction, but this sway is never allowed to develop to any great degree.