You didn't say exactly why or how you are using two PIR sensors. That makes a lot of difference how you use your Boolean operators (among other things). Are they oriented the same direction?
The two if statements are nested in this case so that both must be true in order to execute your commands, but I'm only guessing at your set up.
If you're more specific with your questions, you'll get more specific and relevant help.
void loop(){
distCalc(); // call your distance calculation function for your distance sensor here
if ((digitalRead(PIR1) == HIGH) || (digitalRead(PIR2) == HIGH)) { // if one PIR sensor OR the other detects movement
if (inches <=36 && inches>=12) { // AND if your distance is between two given values
//do something here;
}
}
}
void calc();{
}