How to check if a LED is on?
If the device turning the LEDs on / off runs on 3.3 Volts (has ground to 3.3 Volts outputs), then you might consider directly connecting the 3.3 Volt outputs to the GPIO pins of the ESP8266.  If the device turning the LEDs on / off runs on higher voltages consider either using the appropriate level shifter or the appropriate optical isolator: