Domestic and family violence has been linked to 41 per cent of all murders in NSW since 2013.

Two teenagers killed by their estranged father in Sydney's north will be added to the toll and filed with more than 30,000 other reports of domestic or family violence made to police each year.

The most common targets are partners, but 3459 children were victims of domestic assault in the most recent 12 months of police data, which also recorded 15 murderers in family homes between April 2017 and March 2018. Three of the 15 people charged with murder in these cases were female, most of the offenders were aged between 20-39 and five victims were aged over 60.

There has been a significant decline in domestic violence in NSW between 2008-09 and 2015-16 but the discrete nature of family violence challenges the justice system and family courts have been accused of trying to preserve the family unit ahead of child safety.