A third person has died following Friday's crash near Athy, Co Kildare.
James O'Brien, 85, of Kilkea, Castledermot, Co Kildare was the driver of a car which was in collision with a motorbike.
The two other victims were his 81-year-old wife Betty and John Doyle, 29, from Kilberry, Athy, who was riding the motorbike.
Mr O'Brien's death brings the number of people killed over the weekend to five.
Gardaí have appealed to anyone who may have travelled on the M9 between 1.30pm and 3pm on Friday 31 May and who may have witnessed the collision to contact Athy Garda Station on 059-8634210.