How soon can I accept a job offer?

Wait for EAD.

I'm green card holder, If I obtain french nationality , after 5 years would it be a problem obtaining american nationality?

Don't think you can hold citizenship for all three countries.

The petitioner left dead during the preparation of visa (Immigrant Visa). Would it be a problem with our visa issuance or not?

I'm sorry to hear about this. As my colleague mentioned, humanitarian reinstatement may be possible.

WHAT SHOULD WE DO WE GOT A REFUSAL form FROM The embassy in ANKARA TURKEY ABOUT HIS CR 1 VISA?

You received a standard denial. It doesn't matter that your family members' cases were approved; each case is different. Meet with a local...

I have L1B visa, VIsa expired in MARCH2013.I94 to expire on MAY2014. Applying H1B.

No, unless you successfully obtain a "change of status" to some other type of visa.

Should the job description closely match the discipline of my college degree in order to successfully receive an H-1B visa?

I agree with my colleague. Also, the salary is tied to the particular position in the particular geographic area.

What should i do if my case was denied?

Meet with an immigration attorney to discuss your options. You may be able to reapply.

I agree with Mr. Palant.

How can my husband become legal?

DACA may very well be an option. Meet with an immigration attorney to discuss further.

Where should our marriage ceremony take place as me and my fiance intend applying for a green card after marraige?

I agree with my colleagues - either place is fine. You must have plans on returning to the U.S. with your spouse to satisfy the financial...