Do we need to cancel/withdraw the H4 petition filed in US?

Departure while an application for a change of status is pending is considered an abandonment of that application.

I did'nt availed OPT and got I-20 from other uni. If i defer my admission do I have to go back to my country?

You must be maintaining a full course load to maintain legal status.

I am amercian and my fiance that lives in turkey on a student visa . He is iraqi, we have been together for 4 years never met.

You must be able to prove that you have met in person within the past two years in order to file a fiancee petition.

My H-1 visa 6 year will end in 15 Mar-15 My wife baby deliver date is 10-Feb-15. How i can extend stay 1 month to clear things.

You should consult with an attorney to see if you could recapture any unused H-1B time or other options.

You would need to prove the unavailability of the document the USCIS is requesting to submit alternative evidence of the marriage.

Your employer would need to file a petition on your behalf to obtain an H-2B visa or change of status.

Aos and public assistance

You should answer the question truthfully and explain your answers at the interview.

I140 - if I am the owner of the parent company abroad and the US subsidiary, can I still petition myself under EB1 C category?

Yes, this is possible, however, any changes in corporate hierarchy and structure must be plausibly explained to gain approval of the petition.

Generally, there would not be a problem with that person's immigration status.

I-20 should be in two weeks when can I apply to change my B2 to F1? B2 expired in the middle of August

You can be denied a change of status to F-1 if there is not sufficient time for the application to be approved before classes commence.