UPnP means universal plug an play. Means that any device that connects to the network should automatically set itself up without much intervention meaning you can see all other devices in the network. I would assume Smart Tv's are UPnP.
You could make this really complicated or very simple with minimal extra outlay. Using Windows 7/8 you could share your hard drives to all devices from your computer across a wifi or wired network very easily. A WDTV will read most movie files that you plug into it via USB, or connected via a network cable. As said, your second router thingy should work in bridge mode to give you access to the network All you need to do is connect the Smart TVs to this home network.
(I've got a 6 terabyte HP microserver running Windows Home Server that feeds all my devices including iPads, iPhones, Xbox's, windows laptops and dumb tv's via WDTV boxes, but it's a bit overkill cause I work in IT and I like gadgets)
