A heartbroken Jehovah's Witness whose family was killed in the Margaret River massacre has spoken of his children going to a 'new system' after their tragic deaths.

The bodies of Aaron Cockman's four autistic children - Taye, 13, Rylan, 12, Arye, 10, and eight-year-old Kadyn Cockman - were found at the family farm in Osmington, rural Western Australia, on Friday.

The youngsters, as well as Mr Cockman's estranged partner Katrina, 35, and her 58-year-old mother Cynda, are believed to have been shot dead by the children's grandfather, Peter Miles, 61.

'All my family has stayed strong. We were all sitting around last night and it was not all tears and crying... it was all laughing and happy and joking around,' Mr Cockman said, according to The West.

Aaron Cockman, a Jehovah's Witness whose family was killed in the Margaret River massacre, spoke of his children going to a 'new system' after their tragic deaths

Peter Miles (second from left in suit and blue tie) is suspected of shooting dead his wife, Cynda, (back right), his daughter Katrina Miles (left in red dress) and her four autistic children aged from 8 to 13 (pictured) before shooting himself

'I had nearly tears in my eyes from laughing so much. I've got an awesome, powerful, strong family. They get their strength from Jehovah, and so do I. You might think that is a load of c*** but a lot of my strength is from him, too.

'It might sound weird, but the kids went to sleep and now they are nothing. But to them they are already in a new system. We're just lagging a bit behind here, they are already there. By the time we get there it will all be the same, it is like a time-period difference.'

When asked by reporters about initial rumours that he may have been involved in the shooting tragedy, Mr Cockman said 'bring it on'.

Mr Cockman, the father of four children killed by their grandfather near Margaret River in WA's south on Friday, addresses the media on Sunday

The bodies of Peter Miles, 61, his 58-year-old wife Cynda, their daughter Katrina, 35, and her four children were found at the Miles' Osmington property in Western Australia on Friday

'I think it is funny. I lost four kids. It is not like I don't care anymore but bring it on, let's have a party. You guys say what you want to ask, I don't care any more, I've lost everything,' he said.

'I've got my family but my family they are fine and they have always been fine. I don't want to lose them but I have lost everything in my life. So, you want to ask dumb questions I'm going to answer, you want to ask really good questions I will answer.'

An emotional Mr Cockman revealed the last time he saw his four children alive was when he took them to see The Avengers in the nearby town of Busselton two weeks ago.

'Rylan was sitting down for two and a half hours, [so] we had to go to the park so he could get up and walk around for a bit,' he said.

Three generations were found shot dead at the rural farm in Osmington, 15km east of Margaret River in Western Australia, including Katrina Miles and her four children (pictured together)

'Kat has got disabled [parking] so she can park very close all the time and doesn't have to walk too far.

'Rylan and Kat walk off while two kids are on the little roundabout swing in Busselton, that's the last time I saw them, we had a good time, a great time.'

Mr Cockman described in chilling detail what police had told him about how the tragedy unfolded.

He said Peter had lost a son who took his own life years ago, and couldn't bear the thought of losing the other, Neil, who is gravely ill with a kidney illness.

Peter's wife, Cynda Miles (left and right), was an active member of local community group Transition Margaret River which seeks a happier and more sustainable future and ran her own business

'Peter didn't snap. He's thought this through. I think he's been thinking this through for a long time,' Mr Cockman claimed

'[Peter] went across and shot the kids and Kat first and came back and shot Cynda in the living room. Cynda probably got up, heard the gunshots, she was in the living room. He's come back, shot her.

'He's sent a triple-0 call, made a two-minute call or something which in that call he would have been saying, I'm guessing, about not being able to handle it if something happened to Neil.

'He's gone out to the porch, made the call and shot himself. I don't know how he has done it so well. None of the kids were up out of their beds.'

He said the apparent murder-suicide was 'totally' Peter's decision and speculated about the pressure that had mounted on him in the lead-up to the tragedy.

Mr Cockman's estranged partner Katrina (pictured left and right) was shot dead on Friday

Mr Miles was found with a bullet wound as he lay slumped in a deck chair on the veranda. Forensic teams are pictured at the scene

'Peter didn't snap. He's thought this through. I think he's been thinking this through for a long time,' he said.

'There's no way possible he can lose another son. He's just gone ''right... I can't live anymore so this is it for me. But I need to take out everyone with me because that will fix the whole problem'',' Mr Cockman said.

'And he's fixed the whole problem.'

Mr Cockman said his parent-in-laws were not the 'people you want to get on the wrong side of', and that before being cut off from his children, he and Mr Miles were best friends.

The grisly murder-suicide at a remote farm house (pictured) in Western Australia shocked the nation as one of the worst shootings in the nation's last two decades

Police are believed to remain at the chilling scene where children were among seven people found dead

The pair worked together side-by-side at a farm school where they would butcher sheep ­carcasses.

'We'd go to the high school farm and cut up sheep together... [Peter] was an awesome man, before all this blew up. I haven't talked to them since they cut me off from my kids,' Mr Cockman said.

'I don't feel angry. I feel tremendous sadness for my kids. But I don't want anyone to feel angry. Anger will destroy you. I'm tremendously sad but I'll get through this.'

The grisly murder-suicide at the property, 15km from Margaret River, shocked the nation and has become Australia's worst mass shooting since the Port Arthur massacre in 1996.

Peter and Cynda bought the farm in 2014 and planned to live a sustainable life with their daughter and grandchildren.

Police were met with horrific scenes when they arrived at the 30 acre farm (pictured) with two houses on Friday morning

This image shows the kitchen of the remote farm where a mass-murder suicide was discovered early Friday morning

Nearby residents said they heard gunfire around 4am but dismissed the sound as coming from kangaroo shooters.

A neighbour who lives across the road from the property told Fairfax he hadn't heard anything unusual.

'There was nothing much I could tell [police],' said the semi-retired farmer, adding he didn't know the residents very well.

'I'd seen who I assume was the father out in a paddock one day, on a tractor. But I didn't have the opportunity to say hello.'

Julia Meldrum, deputy president of the Shire of Augusta-Margaret River, told Daily Mail Australia the district was in deep shock.

'It's devastating,' the distressed mother-of-two said. 'It's just shock and devastating for the community.

Julia Meldrum, deputy president of the Shire of Augusta-Margaret River, told Daily Mail Australia the district was in deep shock after the horrific discovery on the remote property (pictured)

Osmington community consists of dirt roads similar to the dusty track at the sustainable farm (pictured) where seven bodies were found

'I actually feel like vomiting. The shire has a population of 14,000 people but each town is very close knit.

Jan Walsh told Australian Associated Press they lived in a very 'caring town'.

'There's retired people who live down here, there's ex-farmers,' she said. 'It's just a wonderful place to live and everyone's so friendly.

'You wave to everyone coming down Osmington Road and you don't even know them.

'In Margaret River there's a lot of children and a lot of young families. It'll be devastating for the community. It's touched many people, people I'm sure will know one another.

'The shire will be doing whatever we can to provide support and whatever else we can do in addition... I've got young children as well. It's just devastating.'

Flowers are left next to a police roadblock where police are investigating the death of seven people in suspected murder-suicide

Flowers and a note marked 'Katrina and family' lay at the site where seven bodies were tragically found

Shire president Pamela Townshend said the town would struggle to come to grips with the horror.

'It's an isolated rural area. There's no centre of town. Everyone comes into town to do their shopping,' she said.

'There's a lot of giving each other vegetables, cooking each other meals, looking after each other when they're ill - very connected in deep ways.'

Osmington, about 260km south of Perth, is a 10-minute drive east of the Margaret River township.

The tiny community, which ABS data shows has about 135 residents, mostly consists of farmland properties and vineyards.

Readers seeking support and information about suicide prevention can contact Lifeline on 13 11 14.