The only way you are cooling these houses down at night is if there's a mighty breeze and cool outdoor temperatures... or if you took the entire roof off.

Your theory might sound good, but in reality it doesnt work that way. Temperatures during this heatwave wont even drop below 20-25c at night, opening the windows doesnt magically mean that the inside drops to match outside as well. It takes hours and hours to do so, and by then the sun is back up, heating the houses up again.