You could do that but it would not be helpful to the network since only one of them will be
able to allow incoming connections.
That's not entirely correct. You can give one of them a different port number and open that port on the router, so your two nodes share one external IP address but have different port numbers.
Don't know how well other nodes get along with that, though.
short answer: don't
Maybe that's still the right answer here - your home network connection probably does not have enough uploading bandwidth to support two full nodes, so they will throttle incoming connections anyway. Just staying with one node might indeed be better.
Onkel Paul