Why do I need the internet to create a home network between devices (computers, tv, tablets, printers, etc)?

My issue is this: I have an iMac, Macbook, iPad and AppleTV, and I live w/ others who also have laptops, etc. We have broadband internet connected to a Wifi router, however, I haven't been able to share my music w/ them (through iTunes Homeshare); unless I connect my laptop and desktop using a wired connection I have issues transferring documents, etc.; AppleTV is hit or miss... From what I've read online about similar issues, most responses make it out to be an internet issue. If I have a wireless router that functions just fine, why can't the devices see each other and connect? What does the internet do in this case? Doesn't my wireless router provide a signal (radio or otherwise) that my devices can use? I don't know if having all these devices on the home network competes for bandwidth? If they do it'd be great to create a separate network for them to free up the other that we use to access the internet.

honestly it sounds like your having a basic computer networking problem between all your devices. I would suggest posting questions on an Apple/iTunes forum site and see what they can offer for help, or start reading books on basic computer networks, or find a friend or co-worker who's knows something about networking and have them take a first hand look at your overall setup.