Cath Houlihan, who was Eileen O'Sullivan's niece and Jamie's first cousin, told how all three were "very much involved in community and community activities, looking after neighbours, as well as doing things for each other."
"They were very happy, easy-going people," Cath said, adding that Jamie loved mechanics and that engines were his passion.
"He had a very strong group of friends who just loved and adored him," she told RTE.
Neighbours found the bodies of 56-year-old Eileen and 24-year-old Jamie at their home in Ballyreahan near the village of Lixnaw in north Kerry on the evening of September 7.
The body of Eileen's partner, 63-year old Mossie O'Sullivan, was found near the family home a short time later.
A shotgun was found close to Mossie O'Sullivan's body and all three had shotgun wounds.
The deaths have been treated as double murder-suicide.
Cath was born in north Kerry and spent her early years there, before her family moved to England.
Her mother, Mary, is Eileen O'Sullivan's sister. The families were close, and Cath visited Lixnaw regularly growing up.
She said it was "really difficult" to come to terms with what happened.
"Not in a million years would you have imagined that something like this would have happened, that Mossie would have done something like this," Cath said. "He was a caring, gentle man. What happened was so out of character."
Cath said the toll the tragedy has taken on her family and on the community in Lixnaw had "changed us".
"We're no longer the people we were. We struggle. They're in our thoughts every day.
"There is a hole in our lives that will never be filled. It's the shock and the trauma that we are working through. That's going to take some time," she said.
Norma Harrington whose family and the O’Sullivan’s were next-door-neighbours also spoke about the effects the horrific events had on their community.
Speaking to RTE, Norma said Eileen and Mossie “were always there for their friends and neighbours”.
"Nothing was any trouble," said Norma who was two years older than Jamie. They grew up in each other’s houses and Normal recalled how Jamie became part of a circle of friends at secondary school at Causeway Comprehensive.
He had just finished his training as a welder and had been offered a position with Liebherr, the crane manufacturer, in Killarney.
He was also gifted with engines and worked locally around north Kerry with an agricultural contractor.
"Jamie had dreams and aspirations that he didn't get to fulfil," Norma said.
Norma Harrington, who works in London, as a lead occupational therapist in an acute mental health hospital, was at home in Lixnaw on a break when the tragedy unfolded. She remained at home for three weeks afterwards.
She said she is shocked that, in the days, weeks and months after the tragedy there was no approach from any statutory agency offering counselling or support.
"We were expected to give statements. We were expected to relive what had happened. Not just my family - the whole community ... We didn't even receive a leaflet through the door or a number to call," she said.
"What we really needed at that point was for services to come to our community to provide a space for the community to come to talk about what happened. That didn't happen and I cannot understand it."
Norma contrasts this with her return to work in London, where she was offered counselling by her employer.
"Over in the UK, I have been able to receive specific trauma support, which has been amazing and helped me significantly," Norma said.
"I wouldn't be standing here today, talking, feeling the strength to talk to you as I am, if it wasn't for that. There isn't any question from the NHS in terms of their role and responsibility, so I don't understand why our Government and the HSE aren't seeing that as their responsibility as well for the Irish people."
Instead, Norma feels her community was left to carry the burden of the loss of the O'Sullivan family alone.
"In 2011, there was guidance set out that there should be intense support from the HSE following events such as these," she said.
"That was over ten years ago, and there was nothing: we didn't get a number; there wasn't awareness. We were left with that burden to carry."
Cath has twice written to Taoiseach Micheál Martin, appealing to him to ensure that supports are put in place, for the community in Lixnaw and for communities throughout the country where similar tragedies have unfolded.
"The only support that they have been able to call on is the Samaritans which, while some help, is shameful and disgraceful," Cath Houlihan told the Taoiseach in her letter.
"These people need you and your Government's full support to help them cope and come to terms with what has happened in their small community."
Cath Houlihan and Norma Harrington are calling on the HSE to establish community psychological support teams, to be deployed to areas when such incidents occur.
They are aware that limited counselling is offered by AdVIC, the charity for families bereaved by homicide that is run by families bereaved by homicide. But they say the scale of the impact on a community when there is a murder/suicide demands a response that AdVIC does not have the resources to deliver.
They believe that only the State, through the HSE, has the resources to respond adequately in those circumstances.
"I want to see better provision of statutory mental health services in rural Ireland," Norma Harrington said.
"I want them to be accessible. I don't think it works by always expecting people to come to the services. As we know, there's a lot of stigma in rural Ireland - among the older generation especially, through no fault of anyone's - so the services need to be accessible. They need to be made in a way that people feel comfortable to engage with them.
"I want to see trauma screening for communities after events such as these. I want people to feel supported, so that they can talk about what's happened, that they can be supported to understand what some of the signs of depression might be amongst the community, so that they can look out for each other in an informed way.
"I want people to be aware of what can be done if they are worried about somebody, and not feeling like that is just their burden to hold. Again, these are all very, very simple steps that can be taken."
Both Norma Harrington and Cath Houlihan would also like to see reform of gun laws, to make it mandatory for people who are applying for firearms licences, or applying to renew gun licences, to be medically examined, so that they can be certified fit to hold a gun.
Cath Houlihan said that medical examination needs to include a mental health assessment.
"There needs to be trained individuals who are talking to people who hold gun licences and understanding what's going on in their lives, so that they understand that there are things here that may impact on their behaviour," she said.
Cath and Norma are both adamant that there will be further similar tragedies, unless these steps are put in place, and unless there is dialogue and discussion around mental health and murder/suicide in this country.
"This is incredibly important, to me personally and to my family," she said. "I don't want to see another atrocity like this. I don't want another family to go through what we have been through."
Through her work in the area of acute mental health, Norma Harrington has seen how people who may be at risk to themselves or others can recover, through care and support.
"It isn't a priority for the Government at the moment and that's what needs to change - it needs to be a priority," she said.
"We can't wait any longer. We can't lose any more families in this way and, while we know that maybe these [murder/suicide incidents] aren't always going to be prevented, that doesn't mean that you neglect it and think nothing can be done. There are steps that can be taken, that should be taken and that need to be taken and that is why Cath and I are here today."
The day after the bodies of Eileen, Jamie and Mossie O'Sullivan were discovered, gardaí said they had commenced a criminal investigation.
They described what happened as a personal tragedy for those involved and their families, and said they were not looking for anyone else in relation to their investigation.
Investigating gardaí are expected to submit a file to the coroner for Kerry North, Helen Lucey.
No date has been set for an inquest into the three deaths.