Your cedars do appear to be Port Orford cedar. Unfortunately, it is highly likely that they are afflicted with the root disease Phytophthora lateralis. 100% confirmation of this would require a field inspection or a specimen diagnosis.

Once this disease is present in a group of trees, it is unlikely that any treatments will save the trees. Soil drench fungicides are listed as a possibility for preventing infection of uninfected trees. These can be effective in nurseries and perhaps in highly contained landscape situations. Soil drench fungicides are unlikely to be effective in wider landscapes and there are environmental impacts to be considered with such treatments.

Removal of infected trees and replacement with non-susceptible plants is generally recommended. For more information see http://pnwhandbooks.org/plantdisease/cedar-port-orford-chamaecyparis-lawsoniana-root-rot