Here in New Zealand, the driver licensing system has three stages: Learner, Restricted, Full. Both of my teenage sons (16yo and 18yo, autistic) have their Learner licenses, and are ready to go to Restricted. They live with their mother (my ex-wife) in the same town as I live, and over the past 10 years, I've had weekly contact with them. During that time, they haven't really walked around town by themselves much, nor done much bike riding, despite the fact that we live in a small city. The 16yo lived with us for a while, during which time he biked a lot more, and had a paper delivery run. The autistic one doesn't like cycling very much. This means that neither of them have very developed spatial awareness. I'm autistic too, so I also struggle with it sometimes, but I've learned to be very aware when driving (also, I biked everywhere when I was their age). The 16yo especially keeps asking me for driving lessons.
Here's the problem: I share my car (which I bought) with my partner, their step-mother, such that we consider the car 'ours'. Since the boys don't have much experience on the road, she thinks that they're not 'ready' for lessons (even though they've had a few with their mother). She insists that until they have walked/biked the streets a lot more, they don't have the awareness and road skills necessary for driving. On the couple of occasions that I have given them lessons, she's admonished me, citing their lack of awareness as reason they're not ready. I've put my 16yo off without giving a reason when he's asked before (such as "not today, ok?"). Her children grew up on a farm, so they started driving quad bikes when they were pre-teens. Driver training is generally outside my budget, so it makes sense for me to give them lessons.
I don't know how to approach the situation. Do I tell the boys that I can't teach them? Do I try to convince my (very strong-willed) partner that I should? And how would I do that? Any other ideas?
Edit to add: I bought the car before my partner and I met, so legally it's mine.