Please do not stress yourself or your son out over this. If the doctor has checked him and given him a clean bill of health as to urinary problems his godmother needs to back off.
My younger son is now 16. He was a late potty trainer between ages 4 and 5 and continued to have accidents - because he sleeps so soundly - until he was almost 13 years old. This was so different from my older son who potty trained early and slept without diapers early as well.
We had him checked for all kinds of conditions, we stopped fluids 2 hours before bedtime, etc all to no avail. I refused to use that pad that gives a small electrical shock because I felt it was cruel. He would get upset every time he had an accident and it was heartbreaking. We concentrated on minimizing his bad feelings.
If your son needs the pullups then use them. That is why they make them, because there is a need. Your son is unique from all other children and noone should make him or you feel bad about this.
You say he is super smart, my son as well has a very high IQ and near perfect grades in school and now in his junior year in high school has already completed several college credit courses. His mind has always worked hard and his body sleeps very soundly.
If there is no physical problem with your five year old the bed wetting will fix itself when it is time. Just make him as comfortable as possible in the meantime, and do not make him feel or let his godmother make him feel bad about this situation.
He IS only 5 years old for goodness sake!