Use serial & AT command simultaneously

How can i use AT command in nodemcu , as i don't want to use library .
But simultanously i have to use serial port for my sensor.
I tried sofware serial for sensor but some error so serial only i can use for my sensor,

i am confused as At command also goes throuch serial.print to nodemcu.
how esp8266 wifi library does it ?

My goal to use ESP8266 AT command & serial simultaneously :

(I don't want to use wifi library & software serial as it slowing my code.)

could someone pls help me? Thanks