Unless I'm mistaken, you WILL need a router and either WiFi or Hard Wired (Category 5) cabling.
Generally speaking there is only ONE Modem on a Cable connection. That modem provides an ethernet jack or jacks to connect your computers/devices to the Internet.
1. Cable Outlet -> Modem -> LinkSys Router -> Cat5 to your PC
2. LinkSys Router->Cat5 to your Magic Jack
1. Cable Outlet -> TV
2. WiFi card in Wife's PC connects to the LinkSys
Cable Outlet -> TV
Honestly, I'd probably put a WiFi card in your PC and put the Modem and the Router in the living room, with the Magic Jack connected to the router. Then I'd grab a dual headed cordless phone setup (make sure it's not a 2.4 GHZ phone) and put the base station in the living room and the handsets wherever convenient.
I may be misunderstanding your configuration, but this is how I'd expect it to be setup.