125kHz RFID and NFC simultaneously
As far as I know, NFC tech operates within the 13.56Mhz band. 125Khz and 13.56Mhz are far enough apart that there should be no problem with both readers active at the same time, as long as your code can handle it. An NFC reader reads only tags operating within its frequency range and the same goes for the 125kHz reader. So each reader will operate without interfering with each other.