Laurence (Larry) and Martina Hayes from County Westmeath were among 38 people killed when a gunman opened fire at a beach resort in Sousse last Friday.
The other Irish victim was mother-of-two Lorna Carty, from County Meath. She will be buried on Saturday.
A minute's silence is being held across the UK at noon to remember the victims of the massacre.
It is understood all three bodies were returned to the Republic of Ireland early on Thursday.
On Thursday evening, large crowds gathered in Athlone to pay their respects to the Hayes at a funeral home in the town.
Colleagues of Mr Hayes, who worked in Bus Ã‰ireann, later formed a guard of honour as the remains were brought to the nearby St Peter's and Paul's Church.
Mr and Mrs Hayes were in their 50s and had one daughter.
A requiem Mass for the couple will be held at 11:00 (local time) on Friday.
Ms Carty, who was in her 50s, was on holiday with her husband, Declan, when the attack happened.
Her remains will be removed to the Church of the Assumption, Robinstown, on Saturday morning for requiem Mass at 12 noon.
Candles will be lit and the names and photographs of those killed will be displayed inside St Anne's Cathedral in Belfast, as prayers are said to coincide with the silence at midday.
Eight suspects, remain in custody on suspicion of being directly linked to the deadly attack. Four others who were held have been released.
Many of the 30 British people who died have been repatriated.
The funeral for two of the three Irish victims of last Friday's terror attack in Tunisia is due to take place later.