Western Australia police said Monday the "five people killed were twin two-year-old girls, a three and a half-year-old girl, their mother and grandmother".
The ages of the children and their relationship to the two adult women found at the Bedford address were confirmed on Monday by WA Police.
"The homicide squad now have teams of detectives on the ground, accompanied by specialist forensic police who are meticulously working their way through this crime scene".
A man in his 20s surrendered himself at a regional WA police station, before officers visited a home on Coode St in the suburb of Bedford.
"It is a tragic thing when incidents like this occur", he said. Two months earlier, in a small Western Australian town, a man shot dead his wife, daughter and her four children in family murder-suicide. No further information was provided on the victims and the man in custody.
Locals said children were often seen playing in the front yard of the home.
Police have blocked off the road near the home on Coode Street in Bedford.
Mr Steel added: "I can say there was at least one woman but I can't say more than that I'm afraid".
"It's horrid to think that in such a attractive area, that's calm and so quiet, that something so tragic has taken place", she said.
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Maria Manfredini, a long-term resident in the area, described the incident as "tragic on every level".
"This is a tragic event that will have no doubt have an impact, not only on the family and friends of the deceased, but for the whole of the community, those first responders who were faced with attending a scene with multiple deceased people".
No charges have yet been laid.
"Just a normal family, you would never imagine anything like that happening", he said.
Three firearms were located at the scene belonging to grandfather Peter Miles.
"She was such a lovely person and such a go getter and hard worker", she said.
The tragedy comes after a 19-year-old man was charged with murdering an eight-year-old boy, a 15-year-old girl and their mother at Ellenbrook in July.
When officers went to the house, they found Michelle Petersen and her son, Rua, dead, and her daughter Bella in a critical condition.