I would never recommend anyone "teach" someone to drive if not in a dual control car as a professional - far too dangerous, unless you live on a large private estate and even then it's still risky. If nothing else, the cost of the car plus insurance etc. is likely to be more than the cost of the lessons.
Once competent, giving them practice in the car they will drive after they get their licence, is a better idea but still expensive if they have difficulty passing the test - and this is from personal experience with a number of family members.
Of course, I'm biased having passed first time after a total of 7 lessons and 13 hours driving time in only the instructor's car!