H1B Transfer - RFE

[SenZ]

Hi,

Currently I am working in Employer A [Service based company] with Client ABC in H1B Status.
I got an offer with Employer B and Applied H1B-Transfer via Premium Processing. I told to Employer-B that i will join once h1b transfer approved.
Now, i got an RFE. USCIS Requested for Client Letter, SOW and Org-Chart details.

Now Employer B asking me to join with their company and client project. Then only client will provide Client Letter and can submit the details which requested by USCIS.

I have few clarifications.

1) If i join with Employer-B, can Employer-A can revoke/withdraw my H1B? 
    1.a)If yes, is there any fee for revoke operation?
    1.b)If my current H1b Revoked, How long i can stay in US?
    1.c)If my current H1B Revoked, as i have another H1B transfer petition is in progress, can i stay till the result?
2) Employer-B need to produce Client Letter, SOW and Org-Chart details.. Is it must to join with the Employer-B / Employer-B-Client to get the Client Letter and SOW and Org-Chart details?
3) I am currently planning to join with Employer-B once H1B Transfer is Approved. But before approval, Employer-B is asking me to join before approval. Is this safe to join?
4) I have another offer with Employer-C in pipeline. Can i process it in parellel with Employer-B. Will it make any issues now or in future?

Please advise me.

Additional Note:
Employer-A Amendment is in Progress. 
I have 11+ Years Exp in Software Development
I completed MCA [Masters Degree], previously Bsc Computer Science.
Employer-B offered 125K

[pontevecchio]

1. If any H1 employee leaves, the employer HAS TO revoke that H1 petition. Nothing new. This was always so.

You can stay based on the timely filed "transfer"

2. Did not B tell you exactly what you are asking?

3. If you do not join, you can stay with A as B has made his approach clear. Safe is a relative term.

4. You can have any employer file your H1 and on approval leave and return with the H1 visa.

[JoeF]

When you leave employer A, the employer is required by law to inform USCIS of the fact that you left. This is mandatory. It doesn't cost employer A anything.