Ok, so the QoS needs changing, Remove the Single Xbox rule as that is incorrect.
Leave the multiple xbox rule. Thats set up correctly. I would ensure that all xboxes have reserved IPs with the following: 192.168.0.100, 192.168.0.101, 192.168.0.102
Then just change the 192.168.0.106 address to .102.
While you make the changes, ensure the xboxes are turned off.