DAG design question, and Powershell cmdlet required to perform DR. Exchange 2013 version

Hello MS team,

I am about to propose the following design to my client. Client has 2 physical sites. One in US, and the other one in Canada.

Site 1

2 CAS

2 MBx servers

DB1, DB2, DB3, DB4 DB5.. DB8, are active databases residing on the 2 MBX servers in site 1

Site 2

2 CAS

2 MBx servers

A passive copy of DB1..DB8 resides on this servers

A single DAG has been created to host all DBs, . All the CAS servers must be placed behind a load balancer

Here is my question:

if we lost 1 MBx on each site, all DBs must be failover automatically to other site, assuming there is WAN connectivity. Here i need to know, what are the powershell cmdlets to make sure all dbs are fully failovered to second site. Any extra task to be performed? Here I assume, that we have quorum to failover all DBs

Second question:

If we lost WAN connectivity, tell me how can I validate all emails will be restored on site 1, and all users will be using site 2. please provide additional steps and powershell cmdlets to failover, and advise if I need to create a second share witness to something has to be done on outlook or dbs to restore email flow on second site. once the WAN access is restored, what are the failback tasks, cmdlets?

Consider also DNS, autodiscover, and mobile devices, any task that must be performed to restore services