As someone that ended up being the teacher for the majority of my friend group. If you are struggling with the teaching more than likely you're trying to give answers to their questions. Which is actually more unhelpful than helpful.

If they're asking you how to make a certain kind of turn, or how to know how close they are to something. Just giving them an answer isn't really useful because they don't know how to arrive at that answer, instead you need to help them ask the correct questions.

" you didn't quite make it in that parallel park, get out and take a look at where the car is. The back of the car is only just barely in the spot, so clearly you didn't end up deep enough in the spot. What do you think you need to do to change that"

And have them keep practicing until they start to figure it out, it will seem frustrating for them in the moment but it's genuinely more useful for them to try things on their own and attempt to reach the answer. than it is for them to be handed the answer, because then they understand not just the answer is, but the why of the answer. Why did I not make that turn, what does it feel like to not make the turn properly. Which is very important for being able to apply those same principles of vehicle control to other situations.

One of my favorite things to do with people is to set up some cones or a block of wood or whatever and just tell them to try and park as closely as possible to that object without touching it. I have them do that, get out, go look at how close they were to it, and then try again if they were nowhere near it until they can get it to Within less than a foot. Great way to help train sense of vehicle position.