The father of the four children murdered by their grandfather in a mass murder-suicide tragedy has broken his silence saying the kids were found dead in their beds.

Aaron Cockman, the estranged husband of Katrina Miles, who was murdered by grandfather Peter Miles, said he doesn't feel sadness for his kids because he doesn't want anyone to be angry.

Peter Miles, his wife Cynda, daughter Katrina and Mr Cockman's four children - daughter Taye, 13, and sons Rylan, 12, Arye, 10, and Kadyn Cockman, eight - were found dead at the Miles' Osmington property, northeast of Margaret River in Western Australia on Friday.

"Peter didn't snap, he thought this through," he told reporters today.

"All the kids died peacefully in their beds.

"How the hell Peter did that I still can't figure out, but he did a good job, he did a really good job."

His eight-year-old son, Kadyn, was sleeping in his mum's bed and was found dead with her.

Mr Cockman said he had not spoken to Peter and Cynda "since they cut him off from the kids" but being angry served no purpose.

"I had so much anger in the last few years," he said.

"The anger towards them now, is completely gone, I don't feel angry, I feel tremendous sadness for my kids, but I don't want anyone to feel anger.

"I still love who Peter was. If it wasn't for him, I wouldn't have Katrina, I wouldn't have her kids.

"I got on so well with him, he was like my best friend.

"But is mental attitude, if you get on the wrong side of someone, there are some people you just don't get on the wrong side of, and this happened to be Peter and Cynda.

"So it's not some random guy off the street who's taken them away from me - he gave them to me and now he's taken them away.

"If it had to happen, there is no better person than that."

READ MORE: The family killed in the Margaret River mass murder-suicide

The four children lived on the Osmington property with their mother and grandparents and 9NEWS understands a number of them were autistic. The children were home-schooled by their mother.

"The kids are beautiful kids," Mr Cockman said. 

"Kadyn was at the age where he would still come up and give me a hug.

"I hope my family stays strong, I know we will, we were all sitting around last night and it wasn't all tears and crying, it was all laughing and joy.

"I nearly had 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."

"A lot of my strength is from him to."

Mr Cockman said the last time he saw his kids, they all watched a movie together. 

"I will always remember their personalities," he said.

"It's not like they died as a baby and I didn't know who they were.

"It might sound weird but the kids went to sleep and now they are nothing, but to them, they're already in a new system.

"We're just lagging a bit behind. They're already there. They'll all be the same. Just like a time period difference

"The last movie I watched with them two weekends ago was Avengers and the kids loved it.

"It's not a good time, watching a movie with kids, I get to be with them, see their reaction but it's not talking, conversation time.

"But I had a great time with them, Taye asked for money for shoes.

"I gave them all a ten dollar note each - I gave Taye a 20 - they never spend it but knowing they had their whole little wallet - independence - I couldn't wait for them to leave the farm situation and be their own independent people. "

Peter and Cynda Miles were well known and respected in the Margaret River community. Police say three firearms were found on the property were owned by grandfather Peter Miles.

Police received an emergency Triple Zero call from a man at 5.15am on Friday that lasted around two minutes, before arriving to the property and finding all seven people dead with gunshot wounds.

"This is a complex criminal investigation," Commissioner Dawson said.

"We are treating this as a matter in which clearly six persons are subject of a homicide crime scene. There is a seventh person deceased."

The local government in the area has also established sessions with counsellors and psychiatrists at the Margaret River community resource centre, where mourners can also offer flowers and their condolences.

The small town of Osmington is a rural suburb about 20 minutes from the West Australian tourist hub of Margaret River.

According to 2016 Census data, it has a population of just 135 people and is mainly known for its vineyards and farms.

Peter and Cynda Miles described their family property in the rural town as “our forever farm”.

“It is here that we will grow as much of our food as we can, sit on the veranda and watch the birds, and watch the grandchildren immerse themselves in the animals and everything else that happens on a daily basis,” a website dedicated to the farm said.

Readers who are seeking assistance can call Lifeline on 131114 or beyondblue on 1300224636.

Anyone with information that may assist in police enquiries have also been urged to contact police or Crime Stoppers on 1800 333 000.

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