One of the occupants was Ann Marie O’Connor, aged 45, from Kilbrogan, Bandon. She had six children and one grandchild and was originally from Worlds End, Kinsale.
She was a younger sister of Catherine O’Connor who was last year convicted of the double murder of two men in West Cork in November 2011.
Her partner, John Paul Carroll, aged 31, from Farranferris Park, Farranree, also died. He was the father of two sons.
He had numerous criminal convictions for minor offences, ranging from drug possession to theft.
Last year Mr Carroll pleaded guilty to possession of cannabis for a third time.
In 2008, Mr Carroll pleaded guilty to several charges after he was arrested when he crashed through a Garda checkpoint while drunk and uninsured. On that occasion he was picked up after trying to flee on foot.
On Saturday at 12.30am the red Hyundai they were travelling in was passing through Ballinahina, when it hit a ditch and overturned.
The car became airborne and the pair appear to have died instantly. Their bodies were taken to Cork University Hospital for postmortems and the road was closed to facilitate investigators.
Gardaí have appealed for witnesses, or anybody who spotted the car on its journey, to contact the station in Mayfield on 021-4558510.
Three hours later, in a separate incident, a pedestrian was killed in a hit-and-run on North Street, Swords in north Dublin.
The 50-year-old victim died at the scene but the car drove off. A 29-year-old man was later arrested and held for questioning at Swords garda station.
Gardaí have asked that two women who took a lift in a dark Volkswagen Golf in Swords between 3am and 3.30am on Saturday to contact them on 01-6664700.