I am sorry to hear about your husband’s medical problems. Actually Benicar causes hyper uricemia (increased uric acid in blood). This can cause stone formation in kidney. It may take years for the stones to form. Please get his serum uric acid tested. Doxycycline is unlikely to be the cause of stone formation.
The medical advice given should not be considered a substitute for medical care provided by a doctor who can examine you. The advice may not be completely correct for you as the doctor cannot examine you and does not know your complete medical history. Hence this reply to your post should only be considered as a guiding line and you must consult your doctor at the earliest for your medical problem.