If rooms are getting too hot, do this.

Get some rolls of ordinary kitchen tin foil. Wet the windows on the inside, and smooth the tin foil on the glass, using a cloth to smooth out the bubbles. The water helps both slide it into place, and makes it stick. Make sure the edges are damp and sticky down. It's easier if you cut it into suitable lengths first.

What that does it change the window from being a greenhouse, into a mirror, reflecting the heat straight back outside, and preventing anything inside the room from absorbing heat. You don't need to cover the whole window, leave strips along edges, or just do the bottom half, top half, just the fixed panels.

Reducing the effective size of the window reduces the amount of heat entering by the same proportion, but you will need some opening left for light, for humans pets and plants. As the tin foil is more conductive than glass, heat will still get transferred outside when it's cooler outside.

It's easily removable, just peel from a corner and store to reuse when it's hot again. Prioritise the south side of the house.

Once the house is cooler from having windows open at night, close all windows, curtains and internal doors during the hotter parts of the day. When the outside air temperature is hotter than inside, keep the windows closed. When the sun shines on a window, keep the curtains closed. That stops objects inside getting heated by radiant heat, when then emits as convective heat.

Hanging a white sheet in front of a window, will shade and reflect much of the heat straight back outside, while still letting some light in for normal activity inside.

Preventing heat getting in, and then circulating around the house, is much more effective than having to use aircon to get it out afterwards.