Two SD card interfaces on one ESP8266?
Not possible without changing the library code. Because the current library code is written intended for only one SD card, ie not intended for multiple SD cards because it will be complicated to do so. The SPI library also uses FatFS library, which is a bottleneck in this scenario.

Worth a try.

sdfatlib is library written for Arduino. I have never used it, but you can give a try on ESP.

Let us know if it works.