2 Xbox One on the same network = network problems?

I'm with a friend right now and we're trying to get into the same session in Red Dead Redemption II but one of us always has an Open NAT type and the other one strictly someone knows a trick how we can both get an Open NAT type?

Since everything runs over ports and you can only assign each port once, the router can only forward the data arriving at one port to ONE Xbox…

This port is then occupied and the 2nd Xbox is unlucky because it also wants to use this port…

Nonsense.

Dream on…