Your computers are in an internal network behind a NAT based router.
Only the router has a public IP address. You can access your internal
network computers via the Internet. To do this you need to configure
'Forwarding' on the router/firewall. Configure the router to forward
connections from a port on the router to a specific IP address and
port (Radmin server's default port is 4899) of the target computer in
your internal network. You need to assign a port on the router for
every computer you need to access. The router will then forward the
connection to your computer in the internal network.