How do I become a driving instructor?

I'd like to become a driving instructor, independent. Could you tell me the cheapest way?

Can my son's friend legally teach him to drive using his car?

My son is working from home during lockdown, so is his flatmate. They have a bit more time available without their commutes so his flatmate has offered to take my son for practice drives. Is this allowed?

I'm in my 60s and getting ready to take my test - which car would you recommend for me?

I'm in my late 60s and getting ready to take my test for the first time in a few months. Which car would you recommend for me to buy please?