A nine-year-old boy and a 21-year-old man have been found dead.
The pair, who are understood to be brothers, were discovered at Banada, Tourlestrane, near Tubbercurry, Co Sligo, yesterday evening.
The young boy was found in the house with stab wounds, gardaí said.
He was removed from the scene by air ambulance and taken to Sligo Regional Hospital where he was pronounced dead a short time later.
The man’s body was found in an outside shed.
Detectives leading the investigation are not seeking anyone else in connection with the deaths and are treating the incident as a murder-suicide.
Gardaí said the State Pathologist’s office has been called in to lead investigations into how the two deaths occurred, and the scene at the house and shed has been sealed off to allow for further forensic examinations.
The family are said to be well-known, moving from Tubbercurry, where the parents were originally from, to the more rural Banada area.
There were four children – the nine-year-old and 21-year-old who died, a teenage girl and a three-year-old boy.
The family home where the tragedy unfolded yesterday was built by the father, who has worked in the building trade for most of his life.
The home is a few miles off the N17, the main Sligo/Galway road.
Gardaí remained at the scene throughout the morning.
Post-mortem examinations are being carried out on the bodies at Sligo hospital.
Jerry Lundy, a Fianna Fail councillor in the area who knows the family, said they need time and space to deal with the tragedy.
“Banada is a quiet, rural area. Unfortunately word broke this morning of a sad, sad tragedy. All I want to say is my heartfelt sympathies go out to the parents and the family and the community,” he said.
“It’s something you hear about in other countries and cities but not in a quiet rural area.
“The community are shocked. It’s a sad, sad time for the parents.”
Mr Lundy said he will meet some of the relatives to express his condolences in person.
“It’s a time we must give a bit of space to the family, especially the parents,” he added.