Twisted father who shot dead his son, 19, and the teenager's girlfriend in front of horrified children at a family gathering faces life in jail after pleading guilty to murder

The appropriate sentencing discount for a South Australian man who shot dead his son and his son's girlfriend will be a key issue in prosecution submissions, a court has heard.

Pawel Klosowski, 46, of Mount McIntyre, appeared in the Supreme Court in Adelaide for the first time on Monday, after pleading guilty to the murder of Lukasz Klosowski and Chelsea Ireland, both aged 19.

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

Pawel Klosowski , 46, of Mount McIntyre, appeared in the Supreme Court in Adelaide for the first time on Monday

Klosowski pleaded guilty to the murder of Lukasz Klosowski and Chelsea Ireland, both aged 19

While he faces a mandatory head sentence of life behind bars, the court was told Klosowski had first admitted his crimes when SA laws allowed for up to a 40 per cent discount on his non-parole period for guilty pleas.

Those discounts have since been reduced under new legislation.

However, prosecutor Kos Lesses told the court that a 'hot off the press' appeal court decision, which found a judge erred in giving the full discount to a child sex offender, 'is likely to loom large in this case'.

The Ireland family previously described Chelsea and Lukasz as great mates who had 'just bonded'

Justice Anne Bampton said she was aware of the case concerned.

She ordered a pre-sentence report for Koslowski, to cover his personal circumstances, family and employment history and other matters touching on his physical and mental condition at the time of the offences.

She also set down February 12 as the deadline for the prosecution to file its factual summary in the case and listed the matter for sentencing submissions on March 22.

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

A number of family members were present in the court on Monday and were expected to present victim impact statements during those submissions.

The Ireland family previously described Chelsea and Lukasz as great mates who had 'just bonded'.

Defence counsel Nick Vadasz said he was seeking at least one further expert report with an appointment made for his client to see a psychologist in early February.