Here are the Xbox Live ports:
- Port 88 (UDP)
- Port 3074 (UDP and TCP)
- Port 53 (UDP and TCP)
- Port 80 (TCP)
http://support.microsoft.com/kb/908874
Port forwarding can only open them up to one console at a time, so it will not resolve your multiple consoles NAT problem. I still advise reading the links in my last post.