Let's start by making sure you talk to your employer's lawyer and NOT some NON-ATTORNEY in HR. Q: 1) Is there any legal way to stay in US as my...

Not really an immigration question. Talk to a divorce lawyer. For the immigration part, if you get a divorce, she will no longer be on H-4 and...

I agree with my colleague, it is up to the laws of your country. Some countries require that you prove you're legally in the US ... some don't...

Is it possible for me to move from H1b visa to F1 vis based on the following conditions?

I would NOT file for F-1 ... you have too many 'immigrant intent' problems. Get the H-4 instead.

Is it an offense?

I agree with my colleague. Even if it isn't "visa" fraud, it can still be 'normal' fraus.

No, they do not have to have the same title .... AND considering the fact that titles aren't important, the job descriptions can be different also.

Can I file new h1b transfer immediately after getting denial and previous h1b was revoked by old employer, have valid i94?

I'm not so sure that your I-94 is still valid ... just because it 'looks good'. Insist that the new company let you talk to their immigration...

I am outside the US with advance parole. I just received to my mail in the US my greencard. Can I have that mailed to me?

Enter with BOTH documents and let the CBP officer decide.

Do i need to re-apply i-751 as termination of my conditional resident will result to extreme hardship or as jointly with spouse

I agree with Mr. Shusterman ... we need to know more about the denial.

With COVID19 and offices being closed, there is no way to answer your question. Be patient and keep renewing your work permits.