H1B extension & COS to H4 EAD for the same applicant


I am on H1B until Sept18. I want to move to H4 EAD. Can I file for the H1B extension & H4EAD together? Since I would not be able to work after Sept, until I get my EAD, can I work on H1b extension application?

My employer can revoke the H1 extension after I get the H4 Approved. Is this possible?

Please advice how I can switch with minimal gap in employment.