// Checking first sensors state
timeCalculation = 0;
timeCalculation = everyLoopTime - pir_time2;
Your comment is wrong. Wrong comments are worse than no comments. Remove it or fix it.
You set the variable to zero and then a few nanoseconds later you set it to something else. You don't need to press 'clear' like on a calculator. The variable can only hold one value at a time. Just put the new value you want into that variable.
Using one variable to stand for two different things at different times during the program is going to cause trouble. You should really have two of these. You see the generic counter variable i re-used a lot but usually that is in a very local scope - just one for(int i=0; ...) so the value of i has no meaning outside of that scope and you can re-use that same name elsewhere for another for loop.
I think I see your problem...
} else {
digitalWrite(led2Pin, LOW);
pirSensorActiv = 0;
}
If sensor 1 has triggered, but sensor 2 has not yet triggered, you will set the pirSensorActiv back to zero. The next time around the loop, you see that the first sensor was triggered recently, so you ignore it. This variable can never get to 2 unless the sensors are triggered within a few hundred nanoseconds of each other.