The questions that you ask are excellent questions and must be asked of the nephrologist who is caring for your son. Minimal change disease (MCD) is a common cause of nephrotic syndrome in young people and often responds within 6 to 8 weeks of steroid therapy. We have a discussion on our web site about MCD at: https://www.kidney.org/atoz/content/minimal-change-disease
There is also information on the National Library of Medicine web site at: https://www.nlm.nih.gov/medlineplus/ency/article/000496.htm
I suggest that you take a list of your questions to your nephrologist and get answers from someone who has examined your son and can give informed answers.