How is he connecting his XBOX to his laptop, with an Ethernet cable and using ICS (internet connection sharing) or bridging network adapters? Or is it some other method?
Does your router DHCP service have sufficient addresses available for all of your devices? If you look into the router connected devices when the XBOX is attached, what IP addresses are being used?
You also may want to use the router QoS (quality of service) settings to lower the XBOX priority once you get the connection issue resolved.