Change of status i-94 Vs initial VISA i-94

I first entered into USA on H4 with stamping and I-94 (say it i94-O) which was later got extended through approval of attached H1B extension petition.

Now, while this I-94 (i94-O) was valid, status got changed to H1B with a new I-94 (say it i94-A) validity period.

While on H1B, I moved from employer A to B through H1b transfer petition. Employer A withdrew first H1B which was through COS and gave me my ongoing I-94 validity i.e. i94-A.

I joined employer B on receipt and petition is still pending. As my I-94 (i94-A) through COS is valid for another 2 years, how long can I work on this transfer petition with employer B?

Also, can I file another transfer petition to employer C while my H1B petition to ongoing employer i.e. B is still pending?

You can keep working for Employer B as long as the decision is pending.

You can file a new Transfer to Employer C too.

Which petition will be used for filing a new transfer petition to C : The original approved petition from company A or the pending petition of Company B ?

The most recent petition should be used.