Problems configure Remote Desktop with port forwarding

I will give you an idea of my set-up then what I am trying to do and what I have done. I have a BT router with Static IP, two wired computers, both have DHCP IP’s but BT Router makes static IP’s assuming computers MAC address don’t change (according to BT) I am trying to connect using Remote Desktop and port forwarding for each PC e.g. 81.149.115.104:51463 The port is open when...