If you are in valid, nonimmigrant status, and your priority date I current, you should file for adjustment of status.

You will want to consult an immigration lawyer before entering a plea. A conviction for DUI should not violate your H1b status, nor subject you to...

How can i proceed?what document do I need to get USA VISA if i am a refugee in Central Africa Republic with my refugee passport

You do not seem eligible for any type of visa to come to the U.S. You could try the UN Refugee Agency to apply for refugee status elsewhere.

Do I need to file DS160 forms using old passport that doesn't have a last name or new passport where the name is split?

Use the passport you plan to present at the interview for the visa.

Deportation

The conviction may render you inadmissible to the U.S., but of course if your conviction is vacated there should be no problem.

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Oath taking letter... Means that my application is approved?

You don't get an oath taking letter for an application for certificate of citizenship. Perhaps you mean an application for naturalization N-400,...

Am I Eligible for EB2 category?If not, suggest me what I need as an extra to get eligible for it.

If you have the equivalent to a U.S. masters, you should be fine for EB2.

$500 to $1500 or so. No, it is not risky to send a FOIA request. You should be filing an online FOIA with CBP.

If he entered legally, his daughter may be able to file for him and he may be able to adjust status in the U.S.

Can a person who had a criminal record over 20 years ago obtain their green card again?

It depends on the precise crime in question as well as the person's current immigration status. Crime or no crime, if a person comes into the U.S....