A Gold Coast mother accused of killing two of her children was "financially motivated" in carrying out "premeditated direct acts of murder", police have alleged.

Maree Crabtree, 51, was arrested at a house in the Brisbane suburb of Coorparoo on Wednesday and later charged with two counts of murder, one count of torture and one of grievous bodily harm.

Police said Ms Crabtree's 18-year-old daughter Erin was found dead at an address in Maudsland in 2012, and the body of her 26-year-old son Jonathan was located in Upper Coomera last year.

The ABC understands police will allege both Jonathan and Erin Crabtree suffered impairments due to the long-term administering of prescription drugs.

Police have alleged Jonathan Crabtree was killed by his mother in July 2017. ( Twitter: Maree Crabtree )

Detectives also allege Ms Crabtree used the same method to torture a woman known to her over a seven-year period.

At a media conference on Wednesday afternoon, Detective Inspector Mark Thompson said the police investigation was extremely complex.

"The family in question have a significant history within New South Wales and other states of Australia," Inspector Thompson said.

He said police would allege the killings "haven't been compassionate acts of a stressed [mother] or a mother at her end, we will be alleging these were premeditated direct acts of murder that have been perpetrated on the victims".

Sorry, this video has expired Police arrest woman in Brisbane over death of two people ( Supplied: Queensland Police )

"The deaths themselves, we will be alleging, were financially motivated.

"The actual method of murder is something that will be very finely picked over in a court of law so I don't want to expand on that at this time.

"These are premeditated and calculated financially driven crimes."

Police allege between March 2011 and August 2013 Ms Crabtree dishonestly gained an insurance payment of $567,863.

Erin Crabtree was allegedly murdered by her mother, and her sister was allegedly tortured. ( Instagram: Maree Crabtree )

She then allegedly attempted to dishonestly gain a benefit for herself through a Sunsuper superannuation death benefit policy of $125,000 between March 2017 and September 2017.

Police further allege she attempted to dishonestly gain a benefit for herself via a total permanent disability claim of $238,800 during that time period.

She made a brief appearance the Brisbane Magistrates Court this afternoon and was remanded in custody.

The mother has been charged with two counts of murder, one count of torture and one of grievous bodily harm. ( ABC News )

Her lawyer Emily Lewsey said Ms Crabtree would be "vigorously defending" the charges.

Inspector Thompson said police were appealing for anyone who may have information to help the investigation.

"Any piece of information, no matter how small can have a significant impact on our investigation," he said.

He said anyone with concerns about the abuse or exploitation of vulnerable people should call police.