1) The sense I was trying for when I used the phrase "knees track directly over the feet" is that the kees should BE directly over the feet . . . not inside or outside them . . . regardless of whether the feet were straight ahead, or turned out.
Another way of putting it: if you could put a camera direclty over your knee while squatting, pointing straight down, the camera should see your toes directly below your kees.
Or another: If you had headlights on both the knees and the toes, they spot(s) on the opposite wall that they illuminate should be directly above and below one another.
What you were describing where your kees "wiggle inwards" under heavy load is exactly what I'm identifying as something to be avoided . . . and yes, it's probably because your 10:30-1:30 foot stance is too much angled out.
I'm tempted to guess that your knees are probably trying to find their angulation for maximum strength on their own . . . and you should take note of that and set your feet to that angle BEFORE you load up for heavy squats. This is probably where you'll be the strongest.
For myself, I have to consciously turn my feet out a bit more than "usual" (maybe to about 11:00-1:00) for heavy loads, because that's where my knees want to go.
2) Man, I had to go look up what the verb "to yaw" was . . . OK, so it's one of the fundamental directions that a airplane can go out of level in: pitch (nose down or up), roll (one wing down or up), and yaw (skewing side to side with wings and nose level).
So, if your pelvis is yawing to one side, I assume that means it's turning (slightly?) while staying more or less level in the same plane?
If so, I bet you are turning so that your stronger leg is forward (for you, turning to your left?), and yes, I bet it's that you are trying to favor, or make more use of, your stronger leg. Stop that. (If it's a PR 1-rep max that you are going for, all right, but otherwise, if it's a "training" set, stop it. You don't want to be favoring one leg, particularly not the one that's already stronger.)
NOTHING about this stuff bores me (well, almost nothing).