Sorry that's a mistake on our part not to make this clear.
So SQL Response has a client and Alert Repository. Client is not licensed so you can install it on as many machines as you like. All the data is part of your Alert Repository.
You need just one license key for each server you are moniroting irrespective of the number of SQL Server instance on it. But licensing takes into considertion your Alert Repository also. So if you monitor the same machine from two different Alert Repository then you will need two license keys.
Please read help or ask us if you need more information.
http://www.red-gate.com/supportcenter/C ... c79499.htm
This is from help page.
Note: If you have installed multiple Alert Repositories, then you cannot share licenses between them. You will need a new license for any SQL Server you want to monitor using a different Alert Repository.
So in your case. I will install the Alert Repository and then register all the SQL Server instance I want to monitor. After that I will install only client on other machines and then connect to this repository.
Hope this helps.