My two ultrasonic sensors are reading inaccurately
I am not sure but may be it helps just by checking principle of working of this sensors as it is depicted for low range distance you must be carefull about reflection from other source of ultrasonic. I think it would be a good Idea to place a delay between these two module so to make sure it get less noise from each other

  FindRange(trigPin1, echoPin1);
  duration1 = duration;
  distance1 = distance;
  delay(1000);//add delay
  FindRange(trigPin2, echoPin2);
  duration2 = duration;
  distance2 = distance;
  delay(1000);//add delay


the other reason for getting zero may be your controller could not measure reflection from wall due to lowspeed sampling (if you are polling) or reading time with low precision so I have a suggestion for you if you are familiar with STM32 there is a built-in hardware implementation for measure time of pulse using timers called one-pulse mode it may helps you get precision you need