Daniel and Damien Duffy were found dead on Thursday afternoon last at the Co Donegal bungalow they shared.
It is believed that Damien, 50, smothered his father Daniel, aged 88, before being poisoned with carbon monoxide in his own car at the rear of the home they shared at Windyhall on the outskirts of Letterkenny.
The father and son will be laid to rest on Monday at St Mary's Cemetery in Ramelton, the village on the River Lennon where Mr Duffy Snr and his wife were originally from.
Daniel and Damien remains will repose at The Eternal Light Chapel of Rest, Mountain Top Letterkenny from 2pm to 4.30pm on St Stephen's Day, 26th December. Family, friends and neighbours welcome.
Their removal will take place from there via Windy Hall and Glencar to St. Eunan’s Cathedral Letterkenny for Reception Prayers at 5pm, reposing overnight Requiem Mass on Monday 27th December
Burial will follow the men's funeral mass at 11am at St Eunan's Cathedral in Letterkenny where both men regularly attended mass.
Mr Duffy's late wife Christina, who passed away in 2009, is also buried in Ramelton.
A family friend said "They will be buried together as they were always together. Daniel idolised his son.
"They were both very decent, religious and highly intelligent men who were great company despite what happened.
"Everyone is devastated and still can't believe what has happened."
The men are survived by Mr Duffy Snr's daughter Anne-Marie Giles, the only remaining immediate member of the family who lives nearby in Killylastin.
The family suffered another tragedy two years ago when Mr Duffy's daughter Caroline (Callaghan) passed away from cancer aged just 48 years.
A post mortem was carried out at Letterkenny University Hospital on Friday but the results have not been released yet for operational reasons.
Both men were described as "extremely intelligent and engaging" by neighbours.
Mr Duffy Snr was head of the ESB in Letterkenny for a number of years.
His son was regarded as a computer expert and often worked in a self-contained flat at the back of the pebble-dashed bungalow.
It is believed that Mr Duffy Snr had not been seen since a week or so ago.
Neighbours of the men said they were both "witty and engaging" and that Daniel simply "idolised" his son Damien.
Damien recently graduated with first class honours in Computing and had planned to do a Masters next year.
Both were huge Manchester United fans and were both season ticket holders often going to matches at Old Trafford.
They also loved snooker and were very creative, often working on building projects together.
A neighbour and lifelong friend said "Daniel and Damien were two of the finest people, hard working, highly intelligent, creative and very entertaining. This is incomprehensible. I am devastated and will miss them terribly.’