You could also consider merge replication, you can combine it with with AlwaysOn https://repltalk.com/2016/05/31/walkthrough-of-merge-replication-with-alwayson-high-availability-2/ or check the Peer-to-Peer - Transactional Replication.

Azure SQL Data Sync is only available for...

Why there is SSO to DB? SSO should be only to app as you have access logic in app. In this configuration you should configure access logic on db level...

There is Peer-to-Peer replication
https://docs.microsoft.com/en-us/sql/relational-databases/replication/transactional/peer-to-peer-transactional-replication?view=sql-server-2017

First check the error log there should be information why SQL wasn't able to accept new connections eg. non yielding scheduler. Depending on the error log there will be next...

MS know best which platforms they support 🙂
https://docs.microsoft.com/en-us/sql/linux/sql-server-linux-faq?view=sql-server-2017

"Microsoft may provide limited or no technical support for SQL Server software components that are...

Hi, this status mean: SUSPEND_FROM_REVALIDATION = Log change mismatch is detected on reconnection (see error log)
https://docs.microsoft.com/en-us/sql/relational-databases/system-dynamic-management-views/sys-dm-hadr-database-replica-states-transact-sql?view=sql-server-2017
looks like replica B was set to asynchronous mode and failover...

You should add ip from the second subnet. Why are you adding ip from the same subnet?

You must provide SAS key in GUI. SSMS is working on your credentials and SQL Server during restore use its own. The same behavior is when you try to restore...

No you don't need a certificate to use TLS1.2. Internally SQL is using by default automatically generated and self signed cert. You need a trusted cert if you use Force...

Error is clear, you are trying to install localized SQL Server, are you sure that this is ENG media as there is 1036_FRA_LP folder?
https://social.msdn.microsoft.com/Forums/lync/en-US/ee93f5c1-6d5d-47a4-b914-31890580188b/sql-server-express-problem-with-instalation?forum=sqlexpress
"With SQL Server...

Hi https://docs.microsoft.com/en-us/sql/t-sql/statements/alter-database-transact-sql-database-mirroring?view=sql-server-2017

"TIMEOUT integer
Specifies the time-out period in seconds. The time-out period is the maximum time that a server instance waits to receive a PING message from...

Hi, you can start SQL in single user mode https://docs.microsoft.com/en-us/sql/database-engine/configure-windows/start-sql-server-in-single-user-mode?view=sql-server-2017
and then add eg: local administrators group to sysadmin role, you don't need to reinstall it.

If you disable them then no, if you stop them then yes. You can check how schedulers are set for them, for distributor it will be start automatically with SQL...

What errors do you have in error log? There should be many errors and information regard this failover that will tell if this was cluster fault or some synchronization errors...

You must change application connection string to chose the driver that support TSL1.2 eg. ODBC 11. Many application use by default "SQL Server" driver that are present on all Windows...