Okay. From a "horizontal" perspective, your knees seem to be retreating to the rear. I mentioned this as well as "thinking them front." Of course they will not go frontward but such actions will keep them from going to the rear.
I have video from 1989 and thru the years. Keep doing as you do. Create the library. It's free to check out the videos and articles. But look at the poster on SQUATTING and you can see what I'm talking about regarding the knees, the grips and the shoes - among other things.
Squatting is it! It's the king! Keep it up and remember "palms under the bar," not on top! Use them to drive, just as if you're doing a shoulder press.
Sorry about the elbow problem.
I can sympathize as I have bad hips and have had subsequential elbow surgery. Work hard, like you're doing, but don't forget to work smart!
If ever any questions .....!
Get yourself a squatting team that meets every Friday. You know the rack will always be available.
Also, there's a saying of "what you love will kill you." This is my take about squatting. "It kills me as it makes me live .... the way I want!"
Sorry to get philosophical but my gym years have all been based on the squat.
Keep using the video. It's a great teacher and you can't beat the memories. I'd say watch them before a session but watching might take too much out of ya.