COS from H4 to F1 - Need suggestions please

[bramaresh 0]

Need advise on the following please:

My son is studying on H4, he is at the end of first year of college.
I have applied for my H1 and H4 extension on Mar, not sure how long it takes and whether there will be any H1/H4 rejections, therefore, trying to understand what is best at this situation.  

1. Can I apply for COS from H4 to F1 while my son is in US?

2. Normally how long it takes to get F1 approval nowadays?

3. Can he start attending college based on F1 receipt or eligible to attend college only after F1 approval notice receipt?

4. Is Canada a suggested option to expedite in such situation?  Will that be quick?

4. Looking at the delay nowadays for H1/H4 extn, we will be on out of status by the time we hear decision on H1/H4 extn and will be staying based on H1/H4 receipt,
   So, I have the following situation to be prepared and greatly appreciate your valuable suggestions:

      Situation 1.        
      If the F1 is applied before current H4 validity and rejection received after H4 validity expiry and F1 is still being processed:
      Question:  Can my son stay in US and attend college based on the F1 receipt? Or does he need Approval Notice?

      Situation 2.         
      If the F1 is not applied till the date we hear H1/H4 rejection and will apply for F1 after hearing from USCIS about the rejection.
      Question:  Can my son stay in US and attend college based on the F1 receipt? Or does he need Approval Notice?

      Situation 3.                                
      If H1/H4 application is still being processed by USCIS, we have decided to apply for F1 before current H4 validity period and let's say it's approved and later my H1 extn is 
      also approved.

      Question: a) Will the H4 get's cancelled automatically as F1 is already approved?  
 
                                   Or  F1 get's cancelled and my son's H4 still get approved? or both run concurrently? Or do I have to apply for F1 cancellation?

                                    In another possibility, let's assume, our H1/H4 extn is approved and F1 was still being processed

                                        Question: In this case, let's assume the F1 approval is received later, will my son's H4 get's cancelled automatically or do I have to apply 
                                                                  for F1 cancellation immediately on hearing H4 approval?
                         

                              b) Let's say father's priority date is current and I would like to change my son's status from F1 to H4 to claim my son under 21 years as a dependent for 
                                  GC purposes, is this possible?  

Thank you for your valuable input sin advance.