Multiple H1B and H4 Extension

My H1B transfer with COMPANY A got approved by USCIS and we filed an H-4 extension for my Spouse.

My Current employer(COMPANY B) and COMPANY A have agreed to allow me to Join COMPANY A ONLY from January 2021.

My Current H1B with COMPANY B is valid only till DEC 12, 2020. So my current employer has decided to file an extension in Premium for me(H1B) and my Spouse (H4) so that i will not go out of status.

  1. Though I already have Approved I-129 with COMPANY A, will applying an extension with my employer(COMPANY B) for both me and my spouse be fine?

  2. Since I filed H4 Extension with COMPANY A, can I skip or not file an H4 Extension with COMPANY B (My Current Employer) or is it mandatory to file H4 Extension Again?