The daughter of the 76-year-old woman and sister of 55-year-old man made the horrifying discovery inside the home on Rosetta St, Rosewater about 1.20pm on Saturday.
Acting Assistant Commissioner Graham Goodwin said she called police after discovering their bodies.
“The daughter of the deceased mother and the sister of the deceased male [was] concerned,” Mr Goodwin said.
“She came around with her daughter … [and] were confronted with the horrific scenes.”
Western District CIB along with Major Crime Detectives and Forensic Response attended the scene.
Mr Goodwin said police believed the alleged murder happened in the early hours of Saturday morning.
The 43-year-old man was arrested, who lived in the same street, was arrested and interviewed by detectives.
“The relationship between the suspect and the occupants of that address is unknown,” he said.
“It is suspected that they were known to each other, but at this stage we don’t know what that relationship was.”
Detectives subsequently arrested a 43-year-old man of no fixed address. He has been charged with two counts of murder and will appear before the Port Adelaide Magistrates Court on Monday.
No other suspects are being sought at this time and the incident is not believed to be random.
Mr Goodwin asked anyone with information or footage to come forward.
“I do ask for the public’s support … with any information that any person may have relative to this event or any dashcam or other footage.”
“That’s not only for events for today, but also for events of the days leading up to these tragic circumstances.”