Pawel Klosowski, 46, of Mount McIntyre, appeared in Mt Gambier Magistrates Court on Monday where he admitted killing his son Lukasz Klosowski and Chelsea Ireland, both aged 19.

Police had been called to his property in August after reports of a shooting and arrested Klosowski without incident.

Speaking to reporters at the scene, Detective Inspector Campbell Hill described the deaths as a "shocking incident to occur in the southeast".

"It's a tragic event and the impacts of this will not only be felt for the particular families involved, and the associates and the relatives, but also for the southeastern community," Inspector Hill said.

Klosowski's early guilty plea could entitle him to a discount of up to 40 per cent on any non-parole period.

His case was not expected back in court until December but was called on late on Monday afternoon.

After her death, the family of Ms Ireland said she was passionate about the environment and determined to "change the world".

They remembered the mechanical engineering student as someone who left a lasting impression on everyone she met.

"Chelsea was compassionate, strong, selfless and fearless and continues to make us proud every day," her father Greg Ireland said.

"We haven't just lost a daughter, we've lost a best friend. Our hearts will forever remain broken."

Debra Ireland said her daughter was passionate about environmental care and making changes to save the planet.

"She was going to change the world," Mrs Ireland said.

"She not only talked about it, she lived it."

The family said Chelsea and Lukasz were great mates and had "just bonded".

Klosowski has been remanded in custody to appear in the Supreme Court in Mt Gambier in November for arraignment and sentencing submissions.

Australian Associated Press