Well, first of all I am not in South Africa! But maybe we can get the ball rolling here anyway. I want to confirm that this is all powered by mains power from an extension cord, yes?
So my first question is about this wind issue. How much wind are we talking about here? I was not under the impression that PIR sensors are sensitive to wind. Which way do you have the sensor pointed? I suppose if the ground was warm and the sky was cooler, and the wind made the sensor or stand physically move, then maybe it could trip the PIR. In that case you would need a more stable stand.
In terms of the parallel PIR setup, I have not heard of that, but I am guessing maybe it is like an OR circuit, where the 2 sensors have to agree to get a trip? I know they make some PIR sensors that have 2 zones in them, but I don't remember what the application was for the 2 zone types.