Multiserver CRM 2015 installation

Hello

Need information on Multiserver installation on following infrastructure.

For CRM 2015 on premise environment we have:-

3 Front end Server - Windows server 2012 R2
1 Backend Server -Windows server 2012 R2
1 Sql and SSRS Server - SQL Server 2012 R2 with SP2
1 Domain server - Windows 2008 AD

Question:

- Do we need to create three different OU in AD for 3 front end servers

- How to link all three front end servers with one backend server with one sql server

- How to maintain user session between all three front end environment

Thanks for quick support

-Rita