I would consider getting Bome Midi Translator. You can create up to 9 virtual MIDI ports to use. On top of that, any MIDI translation needs you will ever have are covered with this piece of software. It’s not free, but it is well worth the money if you’re going to use multiple instances.
I use 4 instances of GP and 1 instance of Reaper, and Bome routes every controller and message to its appropriate location.