Behind the antenna power wall plate, that is in the cabinet above the tv...there should be a spitter that sends antenna to the other TVs. Maybe the previous owner unhooked it.
Or they used satellite, and your other TVs are connected to the sat coax line and not the antenna coax line.
Also make sure the button is pressed in the antenna power wall plate.
Here is the schematic
2016 North Point 341RLTS
520watts of solar. Morningstar MPPT
4 6volt 235ah Surrette batteries
2017 F-350 Platinum CC SRW