The regular Genie line has only 5 tuners and Clients have none of their own, each taking 1 tuner from the Genie to use.

If all you have is the HR54 and the two C61s then you do not have 7 tuners.

With the flexibility of routers now, not only make sure the password is changed on the correct band, but that you don't have a separate network (like a guest network) open on your router. The build-in WiFi (since HR44) of the Genies can use the 2.4Ghz or 5Ghz band if your router supports it. If you've gone as far as changing your router's password, then it should be impossible for the HR54 to connect as it cannot guess a password.