How do we proceed with husband's H1 and my H4 extension application as my COS application for H1 to H4 is not yet approved?

Your husband may premium process the H 1b after approval file the H4

If you are already a US citizen you are not eligible to naturalizeN-400 file for a certificate of citizenship N -600. If unsure consider an...

I want to know, is there any other documents other than the birth certificate she can use to file for me?

Your wife needs to establish her US citzenship. Either obtain a birth certificate or other documentation or retain someone to help.

Report H1B scam to USCIS

Try contacting ICE or the DOL for assistance

I 94 Expiry with valid visa; Passport renewal

Best way to get the proper information is to speak with your employer's immigration attorney

As my colleagues indicate you were not refused

You must answer truthfully. Speak with an immigration attorney.

Iam GC holder.Can my niece come to US from India,on student visa and study in high school here?Can we b her legal guardian here?

Check with the school particularly the DSO if if they have one.

How many days does it take for change in status from H4 to F1 if I go to USA consulate interview in my home country (India)?

Change of status is in US f visa issuance outside. Check proves sings time on CIS website or consular processing times on consular website.

Do my employer need to file H1B Amendment for my case or not?

If your location of employment is different you need an amended petition. You should check with the employer's immigration attorney.