Don't worry about the knees yet and just do these drills before lifting to learn to keep tightness in your core and hips. It may take a month or more until it becomes automatic (depends on how often you practice). You're currently doing goblet squats (if you remove the bar) and the amount of knee travel you currently have is similar to front squats.
When doing back squats keep this amount of tightness while hitting depth and no matter how much you sit back. Remember to engage your erectors, abs, glutes, hip flexors and keep your chest up (learn to use your lats after you have this stuff figured out first). This will keep your spine and hips stable.
I don't worry too much about knee position when back squatting. I only worry about getting the most strength out of my quads, hams and back. IMO, the amount of sit back you use should allow you to get some quad drive and not so far back that your back becomes the limiting factor. Some sit back more than others but the most important thing is to get as much as you can out of all your muscles while using good leverages.
You can also practice engaging these muscles while doing RDLs to help you hinge properly with more emphasis on the erectors than the glutes.