EB-2 Visa Requirement - Previous Work Experience Verification Letter without company signature.

Should be fine, but you might need additional evidence that this person worked at the company at the same time you did and their position there. ...

My husband has filed L1 extension in premium-processeing. My L2 ead is also filed parallel.But he got a RFE.

Yes, it will cause a delay in your EAD. The EAD is issued based on the L1 approval for the principal.

Is applying for receiving cash assistance even when being rejected due to ineligibility considered a public charge (immigration?

These are the questions you have to answer on the I485 adjustment application: Have you received public assistance in the United States from any...

Can a child who is on L2 Visa and completing 21 years stay in US after 21 years when GC processing in progress and has EAD/AP?

Talk to your attorney about the Child Status Protection Act, https://www.uscis.gov/greencard/child-status-protection-act.

Can I attend H1b Visa interview at US consulate outside country without I-612 approval. My H1b is approved?

Your attorney would know the answer to this question, since they prepared and know your case. Ask them before you travel outside the US.

About abandonment ?

Yes, they need to sponsor you as their spouse. Talk to an attorney to figure out the timing and how to file the case.

Am on F1 visa, can I start my own business in usa and get a green card?

Probably not a doable plan. You can look into the E2 visa, you would need to be from a treaty country and have some $ to invest - at least $100K.

What is the quickest way for a Naturalized US Citizen to sponsor Green Card for his younger brother who is above 21?

Focus on helping your brother get a job after he graduates and then having the employer sponsor him for work visa and then a greencard. You can...

I came to USA 4 years ago on L1A VISA, working with same company as Manager for last 8 years. Am I eligible for EB1C Green Card?

Looks like you could qualify, but you need your company to agree to sponsor you. If they don't have an attorney, find one and have a consultation...

Just apply for a passport with your new name, skip getting a new naturalization certificate, its expensive and you won't need it.