You need to check with some RF tester if the keys are working or not (producing a signal)
Maybe the keys are working but they have lost sync with the vehicle (happens if buttons are pressed 20+ times when out of range, which can happen easily when battery is low)
If the keys are working then you can go to dealership or lookup online, the procedure to resync the keys with your car. (You probably have to go to dealership as at least one working remote is required)