L1B to H4 COS

[SSent]

Hi All,

I am on H1B visa (with an approved I-140) which is expiring on Aug 1st 2020.My extention is yet to be filed by my employer. 
My husband is on L1B visa (I-94 expired on Feb) and currently the extension is in progress (pending RFE response by Aug 8th 2020). His 240 days will expire on Oct 17th 2020. Due to the current COVID situation and other VISA restrictions as per the recent executive order we wanted to have a backup option if his extension is denied so that he can continue stay in US.We have a 22 month old kid and it will be extremely difficult for me to survive alone.

My questions are:

1.Can we apply the L1B to H4 COS after his L1B extension is denied ? 
2.In case the COS needs to be applied before his L1B extension decision or 240 days expiry, then should I file his H4 COS along with my H1B extension(regular mode) before 1st August ? or can it be done anytime after my H1B extension(regular mode) is filed ?
3.Till when can he work after his H4 COS is applied?

Please help with the queries.

Thanks in advance.

Edited June 30, 2020 by SSent
added more info