You can find out which terminal is used for NETePay by going to Managers Menu > Register Setup > Credit Card Setup > NETePay is set in the "primary and secondary setup" area.
NETePay only needs to be installed on one terminal, preferably the file server. You can also set the system to a backup SQL connection in case the file server goes down if the terminals lose connection. https://microsale.zendesk.com/hc/en-us/articles/360040485414-SQL-and-Backup-SQL-Setup-Version-9-and-Version-10