Thank you for your request.
Please renaming both devices if you have not yet. Also, check MultiSqueeze that you do not have overlapping names or output devices selected.
When you say they only work individually, does it mean you cannot access or you cannot boot one of the Pi’s when the other is running?
When you cannot access them, can you still see the players in the Squeezebox Server overview?
Are you using WiFi or ethernet cable for connection to your network?
If you can still access the web interface, please copy and paste the Audioplayer debug info here.