Do I need to file a new I-485 when porting from EB3 to EB2 when I already have a pending I-485 under EB3

please address it with the company's immigration lawyers who are well versed with your case

H1B extension beyond 6 year using approved i140 withdrawing pending petition

please address this with your company immigration lawyer as they are the attorneys of record and familiar with your case

Do I need to put (a)(12) or (c)(19) in the eligibility category question of I-765 form?

please see https://www.uscis.gov/working-united-states/information-employers-employees/employer-information/employment-authorization

Do I can use approved petition now?

Based on what you have indicated, that H1b visa to enter the US would no longer be available to you.

H4 EAD renewal

please address with your employers immigration attorney

If you have other documents to show bona fide marriage (joint account, joint insurance, joint lease, being a beneficiary on life insurance, mail...

Are there any Risks Associated with Traveling on Advance Parole while on a 2-Year Conditional Green Card?

You can travel on conditional GC as long as valid.

How much time would I have after the visa expiry to set my affairs in order and leave the country?

You should address this with the employers immigration attorney. In general you should leave before the visa expires (not after). Failure to do so...

What do you advise me to do next or what do I expect from the immigrations ?

At this point, I would await a decision (per the email)(even though you have already waited outside of the processing time.) Processing times are...

Can I sponsor my grand mother (my mother's mother) for her USA visitor visa?

please see http://www.travel.state.gov/content/visas/en/visit/visitor.html this is a good starting point to get basic information.