Margaret River shootings dad wants changes

Aaron Cockman, whose children and ex-wife were killed in a murder-suicide, will lobby the country's leaders to change how courts handle family breakdowns.

Aaron Cockman, the father of four children killed by their grandfather, wants family law changes. (AAP)

The father of the four children killed in a suspected family murder-suicide in Margaret River will fly to Canberra to advocate for a better system for separated families.

Aaron Cockman will on Tuesday join children's advocates For Kids Sake and other groups lobbying in Canberra for a fresh approach when families separate.

"This is all about the kids," he told the Sunday Times.

"Go straight to mediation. Get it all sorted in the same room. Force both parties to be there in mediation and get it sorted."

His estranged father-in-law Peter Miles, 61, is suspected of shooting dead his 58-year-old wife Cynda, their daughter Katrina, 35, and her four children - daughter Taye, 13, and sons Rylan, 12, Arye, 10, and Kadyn, eight - at their farm in Osmington, near Margaret River, on May 11.

He had been involved in an ongoing dispute with his in-laws about seeing his children.

"It's like a constant sadness. My heart drops every time I think about the kids," Mr Cockman said.

He has several meetings lined up, but would also like to sit down with Attorney-General Christian Porter, Prime Minister Malcolm Turnbull and Opposition Leader Bill Shorten.

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