Please tell her not to think that way. Imagine if she had removed the keys and there had been a fire during the night? It’s never a good idea to hide house keys at night - in a smoked filled house you would struggle to find them and you might have come home to a dead family instead.
Regarding your son (I’m only as far as this post I’m reading the thread, so apologies if you’ve made a decision already), I agree with the others and your decision not to ask a police officer friend - it’s a terrible position to put them in. I’m ADHD/ASD myself and have a strong sense of “justice” in me, and think that people should do the right thing etc. BUT I don’t think you should report him to the police in this situation as long as you are 100% certain he isn’t hurt anyone or damaged anything. The risk is that they decide to go hard on him and he does end up with a criminal record, which would really impact his entire future and make him more likely to go down the wrong path. I would see this as a crossroads - whatever you do here will have long-reaching effects.
If you get speeding fines etc through, I would respond to them with evidence that you were out of the country at the time, so could not have been driving the car. I would also state that you had not given anyone access to your car whilst away. Both of these are true. Do NOT say you don’t know who was driving, but also don’t say you do. If they present photographic evidence of the driver then you may need to say it looks like your son at that point.
For your son, I would get him to do some research and create a 10 minute PowerPoint presentation to you, his dad and grandma on the dangers and consequences of driving without a licence or insurance. You tell him you expect to see statistics in there on fatalities, accidents, injuries, prosecutions, what it does to future insurance premiums, etc. He is not allowed to use AI to create it. The hope is, by doing the research himself (and not you just telling him) he will understand the danger he put himself in, that he could have killed someone, that he could have ended up with a criminal record, made himself uninsurable, etc.
I would also try to find some stories yourself to show him afterwards of some worst case scenarios. Maybe even ones where it was teenagers who had licenses but a mistake brought about tragic consequences (eg that car full of teenagers that left the road and I think ended up in water but wasn’t found for a few days - it was all over the news in the last couple of years at some point) to show that even with a license, things can and do go wrong.
I would make it very clear that if it ever happens again, you will take him to the police station yourself to report him for stealing your car, driving without a license & driving without insurance. I’d also tell him
that should you receive contact from the police about your car being involved in an incident on this occasion, you will not be covering for him.
I do think it’s worth trying to get him to articulate why he did it. What made him decide that it didn’t matter that it was wrong? You mentioned about him choosing to pick your car - I’d ask him why. I suspect he knew he was more likely to get stopped in a high powered sports car, or he was more worried about the consequences and punishment if he took his dad’s car.
Was he definitely alone in the car? If he had a passenger, I actually would go to the police (I was writing the above assuming he was alone, but as I was writing about finding out why he did it, it occurred to me he might have picked up a friend).
If be tempted to ask him what he feels a suitable punishment would be. Quite often kids will give themselves a much harsher punishment than we would! But if he doesn’t, you say that’s a starting point but do you really believe that’s enough? Then add whatever else you have thought of. I’d go hard on the punishment because he must not feel like he’s gotten away with this but you not reporting it. You need him to really, really regret this to the point that he would never do it again.