I hate to point this out, but there will be a 3rd person also 'teaching' your child every week - a Teaching Assistant who will cover both of the job sharers P&P time (they are both entitled to this time off every week). So, not just 2 teachers, but 3 different members of staff.............
I have the same issue with my daughter's school. Essentially, a TA teaches the class (on her own) for a minimum of a day per week (often more!) Unfortunately, in the case of her class, on one week she had 5 different members of staff covering her class.
Also, beware the school which ensures that the teacher opens the door to the children (and parents) in the morning, and then quickly makes an exit out of the classroom once the doors are closed to the parents - because the Teaching Assistant is actually their teacher for the day.
I didn't actually believe that this was happening until one day when I was hunting through the lost property along the corridor from my daughter's classroom and saw the teacher making her rapid exit! My daughter had been telling me about it for weeks: "No, I didn't tell my teacher because she wasn't there, Mrs XXXX teaches us" - it went on for weeks and weeks!
Unfortunately, schools won't go out of their way to explain the difference between a TA and a Teacher.