A network-related or instance-specific error occurred while establishing a connection to SQL Server (Virtual Machine)

First time stackoverflow poster,

I have 3 Virtual Machines, all running Windows Server 2012 Standard with IIS 8.0. They are connected through a Tier3.local domain. The VM’s are set up as a Webserver containing the applications, an Appserver containing the data services, and a Dataserver containing the SQL data base. I am trying to get the connection string between the Appserver and Dataserver to connect properly. I keep getting the error attached below, and have tried many solutions including ones found on this website, as well as the ones linked below

https://blogs.msdn.microsoft.com/sql_protocols/2007/05/13/sql-network-interfaces-error-26-error-locating-serverinstance-specified/

I am not sure if this problem is because of the VM's or because of a problem with the SQL server. My connection strings are as followed

Instance Error