Perhaps try attaching a photo of each guitar to the outside of each case in addition to purchasing a cheap decoy, flashy electric guitar with more street value than a CG?
During our years in an area with numerous home invasions, amazingly my violin and CGs always survived untouched. They were my treasured possessions, but thieves went for our tvs, cameras and other electronics.
Although, I am not sure what would have happened had we not relocated. Someone had started to post "Cash for your instrument" flyers near our former home. Perhaps we were experiencing the appearance of a higher class of criminal?
If they are not being used by a professional musician, a rider adding valuable musical instruments to the family homeowners or renters insurance coverage may be surprisingly affordable. For many, it could be worth exploring.