Two things:
1) Your router will only route IP packets for IP addresses within its own "sub net". If you are giving manual IP addresses to your players that are not in the sub net then their packets will not be routed. Better to enable the DHCP service on your router and turn on the players "use DHCP" setting.
2) Every UPnP device has a so called uuid (universally unique identifier). If the device manufacturer has done his job properly then every instance of every product will have a different uuid, but often the device programmers get lazy and use a hard wired number (the assume nobody would have two instances of the same device). If that is the case then UPnP control points cannot differentiate between the two devices, and nothing will work. In that case you need to get the manufacturer to either fix the product or give you a refund.