A:
Only one tv can log into the Slingbox at a time unless Slingbox came out with something new. Today every tv needs a cable box. Slingbox cannot replace a cable box.
Have you thought about dropping cable and putting up an antenna?
Each tv needs to be fairly new with a. Digital tuner. One antenna each tv can watch what they want NBC,CBS,ABC,PBS,FOX,WE,etc.
To get other channels add a Roku-3 to each tv, this give you access to Internet channels, Netfix, Hulu, hallmark,History, and 2,000 other Apps.
You may want to Ali look at SlingTV .