H1B Transfer: question about latest petition and pay slips

Hello, asking this for a friend:

He was working for company A until last week, now he is working for company B… when he was about to leave company A he got offer from company C and they are going to file H1 transfer next week:

My questions are :

  1. Is it mandatory to submit company B’s petition when company C files H1 - company B says they will give the petition after 2 weeks only, by the time company C will file their H1…
  2. Do we need to let company C about move to company B
  3. Is experience letter required for H1 transfer