H1B Transfer query - Urgent

Hi All , I have a query regarding the H1B transfer process . I am currently working in an Indian IT company A and my Visa validity is till Feb 2020 . I got an offer letter from US based company " B " in Oct 2017 . They filled my H1B transfer process in Jan 2018 in Premium but it got denied and then they refiled it again in April 2018 and I got an RFE after refiling and the company “B” has not submitted the response yet . In the mean time , I was looking for other opportunities since the Visa transfer process at company “B” is taking very long time and I am not sure if it will go through . Now I got an opportunity with an Indian based Company “C” and they will file the transfer on premium and I am thinking of Joining company “C” on receipt . I need expert advice to help me clarifying some of my queries 1) Is there any Issue if Company “C” files my H1B transfer while the Transfer is in progress through company B ?2) Do i need to inform company B and C about each transfer process ?3) If transfer is successful for company B after joining company C on Receipt , Can i join company B ?4) If transfer is successful for company B after joining company C on Receipt but transfer gets rejected with company C , Can i join company B ?5) I would like to negotiate with company B for better salary and senior role as it is almost since 9 months offer letter was issued . What is the process involved if the offer letter is changed ( Salary hike and Role change ) … Do company B needs to file amendment for the same while submitting the RFE response ? please advise …Appreciate someone’s response on the above queries Thanks