where do you start with this one . To be honest this is too complex and a bit silly for what you want to do am i right in thinking that what you want is seven machines all as web servers all accessible through one internet connection ???? You cant point your browser at www.domain.com:70 because this will goto the machine with the ip address that matches hostname domain.com port 70. if your using iis you can redirect it to another webserver on your lan but the main problem as i can see it is you internet setup altogether barmy i really dont think you can do what your trying to do besides if you want this machine to be visible permanently your going to need a correct internet ip address from your isp to be static so you can have your domain name configured properly otherwise everytime you register a new ip address with your isp dhcp server youll have to remember to change your webserver settings etc. Why dont you sell all your machines buy a nice big powerful server and run your website of that. Or Pay someone to host it for you might be cheaper and alot less stress.
PS. If your using a DSL connection with no firewall setup in place all machines are probably visible anyway !!!!!!!!!!!
I dont suppose you have a diagram you can post ???