Aberdeenshire-born Hazel Glendinning discovered the bodies of her daughter Heather Glendinning and granddaughters Jane Cuzens, 12, and Jessica Cuzens, 10, at a house in Western Australia on Monday evening.
She alerted the police after finding the youngsters in the hallway and detectives quickly arrived at the property to find a crime scene described as one of the worst they had ever encountered.
Strathclyde Police last night said the men, aged 26 and 32, were detained yesterday afternoon and are expected to appear at Hamilton Sheriff Court today.
A full report will be sent to the procurator-fiscal.
The arrests came after as many as 60 motorists were stopped and questioned by police on Tuesday night as officers stepped up the investigation into the death of the 76-year-old, who died outside his home in Ashgill, South Lanarkshire, on Wednesday, November 30.