Honestly this seems like an unnecessary over complication of the situation. Why don’t you just connect the two newer keyboards, the Motif and the Tyros, directly to your PC through USB MIDI (just have to download the USB drivers). Then use something like a Roland UM-ONE-MK2 (see pic) to connect the older PSR keyboard. I know for certain that the Motif has a virtual editor that you can also utilize if you go in through USB, not sure about the Tyros. If you just do standard midi cables, thru a hub or whatever, you won’t be able to utilize that tool.