First, this should be a new post, as it has different questions than the original.
2nd, you can do what you propose, but the only people who will be able to see those sites will be on your LAN. As you have already seen, with a single address, and your router serving a web page at that address, you'll never get past the router at port 80. You could run the sites on different ports (1 per machine), and forward traffic to those ports through the router to the correct internal address.
You could also turn off webadmin, and then you could forward port 80 to any one computer behind the router.
For named itself, you need to add zones into named.conf, and then add the zone itself into wherever your installation stores zone files. Once that it done, your internal BIND will give the local IP address of those sites to your LAN. You also have to reload/restart BIND once you make those changes, before they will take effect.