The bodies of two adults were found outside a building on the property and the rest were found inside.
Police issued a statement from unnamed relatives of the Miles family saying: "We are devastated by this shocking event".
"We respectfully ask that the community refrain from speculating on the circumstances surrounding this tragic incident".
"The good thing about a small community is that we all mobilise to support people who are in bad distress, and there will be a huge community response ... to support people affected directly and indirectly by this".
Three generations of one family were widely reported Saturday to be the victims of Australia's worst mass shooting in 22 years, an apparent murder-suicide in which seven people were found dead. They all resided at the property, he said.
"We are treating this as a matter in which six persons are subject of a homicide crime scene and there is a seventh person deceased".
Two firearms were located at the scene.
"The loss of any life is tragic, but four children and three adults, this is a significant tragedy", he said.
Police confirmed the father of the children, Aaron Cockman, was also shocked and was being provided with support. Dawson added, "Police are now responding to what I can only describe as a horrific incident".
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"My heart goes out to them and we will certainly provide as much support as we possibly can". Police were led to the property by a phone call before dawn, Dawson said. "Based on what we do know, this is clearly a tragedy".
Detectives from the Homicide Squad and Forensic Crime Scene Unit have travelled to the scene, about 270 kilometres south of Perth, as part of the investigation.
"I won't say what was said in the call".
"Police are now responding to what I can only describe as an horrific incident in Osmington, 20km northeast of Margaret River", police commissioner Chris Dawson said on Friday.
After 5 a.m. the police were called on Friday to the home of Cynda and Peter Miles in Osmington which is a village near the tourist town of Margaret River, 170 miles south of Perth. They were dead from gunshot wounds at a rural property. The young mother was named locally as Katrina Miles.
"It's just absolutely really shocking", he told AAP. I heard quite a few gunshots and at the time I didn't take much notice of it.
One friend said: "I always admired Katrina for her strength".
"There's a lot of kangaroos around so it's not unusual, although not at that time of the morning".