Mrs Campbell's great-uncle, Corporal William (Bill) Goodall, was killed on March 23, 1944, aged 33, and Mr Campbell's great-uncle, Private Gavin Campbell, was killed three days later, aged 35.
Both men came from Oamaru and knew each other and both left young families.
Mrs Campbell agreed it was "bizarre" they were buried alongside each other.
Mrs Campbell had already visited the grave of Corp Goodall during an overseas trip with her grandfather more than 20 years ago.
It was not until she married Mr Campbell that they realised his great-uncle was buried beside her great-uncle.
More than 4200 Commonwealth servicemen from World War 2 are buried or commemorated at the cemetery, 139km southeast of Rome.
Mr and Mrs Campbell, from Campbells Butchery, returned last week from a month-long holiday in Europe, which included the visit to Cassino.
"It was just something we wanted to do. It was amazing.
"It's a very sad . . . very sombre place," she said.
