Will I-130 allow a person to stay in US? I know I-485 is for adjustment of status which authorizes a person to work.

Yes, USC spouses are eligible to adjust status so long as they were inspected upon entry. There are other exceptions too but I don't believe they...

Is H1B amendment with USCIS necessary or just a new LCA for new location is enough?

I don't believe it matters whether you suggest one way or the other. The company's attorney will advise the company how to proceed in this case.

I have 12 days gap in between H1B jobs (or 8 working days). New H1B is approvd. Will this cause any issues for stamping in India

Ideally an attorney should review documents to advise you. The best way to proceed is to seek a full consultation.

H1B extension denied and applied for h1 to f1 transfer before h1 denial. Can I stay in US until Change of status is complete?

Yes.

You do not qualify for extension with new employer as this time. Once this pending petition is approved, another extension can be filed.

What will happen if my H1 transfer is not approved?

You may continue working for Employer A as long as the petition is valid.

2 simultaneous H1 transfers?

I would not lead two companies to file H-1Bs at the same time.

Yes, they can be claimed as dependents on taxes too.

Am I eligible for EB2?

You seem to qualify.

Completed 5 years in L1B and presently in H1B so i will be completing 6 years straight in US. can come back on L1A

You may first want to check with the company's immigration attorney whether you qualify for L-1A, employment abroad rule in managerial capacity, etc.