I got a moderate NAT and server connected on shaw with no ports forwarded with multiple xbox live devices on the router. The first couple always get open and the 3rd get moderate.
I got a strict NAT and server connected on Telus with no ports forwarded. One teen was actively using xbox live when running tests so I expected the strict.
To get multiple xbox live devices all with open NAT my fix has always been to bridge ISP modem to a Netgear r7000 nighthawk, give all xbox devices reserved ips and turn on QOS and UpnP. We have had up to 5 devices online all with open NAT with this solution.