If you are inside the same subnet (192.168.x.x or similar) you should have to port-forward anything as the traffic won't cross the router. You might have a firewall issue in ubuntu though. Try to temporarely disable the ubuntu firewall to see if they connect.

Also, you should try to add each nodes addresses in the debug console using the following command in the two clients.

addnode add

Also disabling the Map ports using UPnP might help.

Hope it helps you.