What components are they leaving? The computer with Blue Iris on it? If it was purchased from someone you don't know, you should be wary of trusting a Blue Iris system left by a previous owner for reasons of privacy. The computer could have any number of backdoors installed. I'd recommend reformatting the drive(s) and reinstalling Windows on it. Before doing that, to aid with restoration, I'd write down the Blue Iris license key (which this tool can retrieve for you), and the configuration details (IP addresses of cameras, user names, passwords, etc) and deactivate Blue Iris to reduce the chance of having trouble re-activating it later. Would not hurt to take a full backup of Blue Iris's settings in case you miss something. The same tool that gets the registration key can also make backups that are fairly straightforward to read in a text editor.
Thank you for the information. They left the cameras, Ethernet switch, desktop computer and their hardware for their internet. We disconnected the internet from the system when we got the house. Still in the process of getting our internet situated.