How to insulate brick/plaster walls from extreme heat?
Add a corrugated roof slanting from 1ft to 2ft high with the corrugations pointing to the higher side. Convection will pull the air to the higher side and out, providing some airflow. 
Insulate the ceilings of your living areas with rigid foam panels to limit heat gain from the roof. Provide awnings above your windows for shading in the summer, especially on the South facing windows, use a passive solar calculator online to size the awnings properly for passive sun heat in winter.