Labor certification in Audit process for 3 yrs

This is definitely beyond processing times.

After interview has been scheduled for AOS, does changing address reschedules the appointment?

Yes, changing your address can affect the location and timing of the interview.

What are the consequences of getting declined once for admitting to one time use of marijuana?

It's the time for your cousin to consult and possibly hire an experienced immigration attorney.

I married in the USA but now live in Mexico and can not travel to the US. I want to get a divorce. Can I get divorce in Mexico?

You can get a divorce in Mexico, depending on their laws.

Can my fiance travel to me?

The K1 visa is strictly a visa tot he United States, only.

What category will it be for the us citizen parent want to sponsor for divorce daughter, F2B or F3 ?

She is considered Single, and under the F1 category.

If I am on h1b and if I open an LLC but after some time if I do a status change to H4 with no EAD. Can I still be as an investor

This question is best answered in a private consultation with an experienced immigration attorney.

Green card petition recently filed. Can parents travel to US on visitor visa? - they already have a tourist visa

Yes, they can but they will need to prove, upon inspection, that they plan to return after a short visit.

Will I be eligible for the 24 months OPT Extension after my degree program has recently changed from non-STEM to STEM?

I agree with the previous answers. Your best bet is to apply for a STEM EAD.

To cross the border, you will need a passport and unexpired permanent resident card.