Audio can be solved with a (cheap) mixer. You can get 24 channels for around 500$:
http://www.thomann.de/de/behringer_sx_2442fx.htm
This will solve all your audio problems with proper equipment attached to it. Here you will have full control over all of your audio sources (analog only!) Specially because people do it for ages right now, every band that is recording songs uses this technology, it is well developed and affordable. You can mix whatever you want there and route it to a couple of different outputs and also to your headphones if you need to manage it. Dont expect the highest audio quality, but this is enough to work without any noise that people get when going too greedy into the audio world.
But for videofeeds you will spend way more money. Capture cards are expensive, that professional stuff from BlackMagicDesign (go take a look, but hold your wallet!)... Thats intense. And this is just the beginning, you need stuff to plug in into these capture cards.
Then you might want a Videomixer (same as DJ-mixer just with video inputs and additional functions) - this will set you back a couple of thousand USD...
Just tell us what the heck is this project and what do you try to achieve.
A streaming PC for each station can (and will) be cheaper than equipping it with highend audio and videogear.