Ms Quinn, her daughter Charlotte, and twins Alice and Beatrix lived at the Coode Street home which is now a police crime scene. Neighbours say the children’s grandmother was also often at the house, helping to care for the children.
Forensic officers remained at the crime scene overnight after a man aged in his 20s went to a police station in Karratha, some 1500kms from Perth, and sent them to the Coode Street property.
The man, who was in custody being questioned on Sunday night, is known to the victims but police have not revealed what he told officers.
It is believed the man also lived at the home, although police have not confirmed this.
“The man currently assisting police remains in custody. No charges have been laid at this time,” police said in a statement on Monday.
Homicide detectives and specialist forensic police are continuing to comb the home for evidence.
“Depending on the size of that crime scene, that will take a period of time and it could be a number of days,” Assistant Commissioner Metropolitan Region Paul Steel said.
A bouquet of red roses with a card saying “rest in peace, neighbours” has been placed on a light pole near the house.
According to her Facebook page, Mara Quinn became engaged in August 2014 and the couple had their first child in March 2015.
It is understood there was a significant age difference between the pair.
A young father, who is building a house nearby, told AAP: “I’ve got a two-year- old girl – I can’t rationalise anything that would cause someone to do that.”