openvpn does not need to be installed on all computers in the house.
There are two components to openvpn the server and the client. Where is the server openvpn located ? Some system have it configured on the router. (ASUS...).
The client openvpn needs to be installed on remoted devices ( tablet, phones, PCs ) that are external to your home network. There is a configuration file that is used to configure the openvpn client. You execute the client openvpn to connect to your local network. Your are now on your home network ,using the local ip addresses of
blue iris system and the port number of the BI web server.
The 81 is the port number configured on the BI web server that will be responded too. IN BI you can change this port number. This is NOT a forwarded port.