Traveler_

As was stated in this thread several times, you do not get police certificates from the US. Not sure what you are filing for after living in the US for 2 years already, but the police certificates are needed for visa interviews, such as the K-1(this thread is posted in the K-1 forum) and spousal visas. Police certificates are needed for anyplace you resided, other than the US, since the age of 16.
http://travel.state.gov/content/visas/english/immigrate/types/family/fiance-k-1.html#6
Police certificates from your present country of residence and all countries where you have lived for six months or more since age 16 (Police certificates are also required for accompanying children age 16 or older)
http://travel.state.gov/content/visas/english/immigrate/immigrant-process/documents/submit/documents-to-submit-to-nvc.html
Note: Present and former residents of the United States need NOT obtain any U.S. police certificates

Many years ago I visited the USA and was given six months, I had applied for the visa and told the consular I would spend a couple of months. I stayed 5 months and a week. That was my second visit to the USA. The next time I applied to renew my visa (via drop box without an interview), I was invited for an interview and promptly denied after just two questions. It is not rocket science to figure out what the problem. In my opinion no visitor should stay the full six months except compelled to by serious circumstances.
 
Four years ago my friend Asare's mother came and on her second visit spent the full six months against my advice. She had a five year multiple entry visa. On her next renewal she was accused of working (the consular officers accusation was entirely based on after all who stays in a foreign country for six months) and promptly denied.
 
The risk is entirely yours if you choose to proceed with this unadvisable course of action. Morocco (I assume that's where you MIL is from) is not an affluent western country, doesn't make sense to take unnecessary chances.
 
PS: Immigration doesn't care if you already paid for a six month ticket, pay the change fee and change it
 

I got marriend in Cancun, Quintana Roo. I found it really easy, as it is a wedding destination, you can just check with a Hotel and they do everything for you, just need to be there 2 days before. 

I'm sure somebody will come up with something better but for starters here is what the IRS has to say about this ( and they're the only reason why insurances want your SSN ). Question 5 answers what to do when you don't have an SSN.
 
https://www.irs.gov/affordable-care-act/questions-and-answers-about-reporting-social-security-numbers-to-your-health-insurance-company
 
So if they're OK with a placeholder then there's no reason why the insurance insist on it.

C21 is credited to the same sub-quota as F21. CX1 is credited to the same sub-quota as FX1. All of them are the same thing, visa issued to the spouse of an LPR, whether it's conditional or not depends on how long you've been married. Whether you get the country-cap-exempt one (CX1/FX1) or not (C21/F21) depends on what visa numbers the consulate has available.
 
In the grand scheme of things it really doesn't matter which code they put you under.

You are confusing family preference categories (F1, F2a, F2b, F3, and F4) with visa classes.  

An F2a case could result in several different classes of visas.  
 
Don't concern yourself with your visa classification.  It doesn't matter.
 
To get a 10 years green and avoid getting a conditional green card which requires filing to remove condition, make sure you enter the US after your 2nd wedding anniversary.  It will not matter which visa classification you get.  It only matters if you enter the US before or after your 2nd wedding anniversary.