Azaleas and camelias will both require acid soils. Any soil that is near buildings or walls will require treatment as both contain lime, which is alkaline. In days of yore plasterers had dumping grounds around the yard for leftover and waste materials so this could be a cause.

I always top up pine needles as mulch, which over time builds up good leaf mould, retains moisture and provides good acidity. The mulch also keeps down weeds. You'll find that azaleas have a root system that is fine and close to the surface so they need adequate moisture to survive and camelias also like moisture.

Camelias are not the flowers that turn black if you touch them.

Cheers

Richard