I see that you don't have room to plant tall trees nor to do lots of earthwork for ground loops.
Close to the equator the sun will mostly be hitting the roof, so +1 on the PV panels. If that is too expensive, build a second roof on top of you roof, raised 10-20 cm, like an umbrella. It will shade and allow ventilation of the hot air already trapped.
Also, do you have an attic, or is the roof directly above the upper floor ceiling? Any kind of insulation will reduce heat gain from above.
Another idea is to make a
ventilation heat exchanger that will allow you to replace stale with fresh air without losing/gaining too much heat, and reduce humidity a bit. Your house would have to be tightened up, but this is also the case if you have any kind of air conditioning.
As for A/C (I saw that you have a unit), maybe hack it a bit? Use a larger condenser (the hot side) and place it in the shade.