I don't know if this is going to work but my only idea is that each DJ is to try DJing in the different modes:
1. PERFORMANCE MODE (USB)
Connect one laptop as normal round the back using the USB cable.
Use Rekordbox in Performance Mode, by pressing LINK button to the left of the XDJ-XZ screen.
2. EXPORT MODe (via Pro DJ link on Ethernet)
For the next DJ Connect the second laptop via an Ethernet Cable (laptop may need an adaptor these days)
- put Rekordbox into EXPORT Mode, wait about 5 seconds
- a button will appear at the bottom of the screen
- [ L I N K ] - press that!
The person using this option will essentially be treating their laptop as if it is a USB device, searching through the playlists but DJing using the screen of the XZ - not rekordbox. Rekordbox is sat there like a dummy device.