Chol Achiek, 12, and Dau Akueng, 15, were allegedly set upon by a group of males at Cobblebank, in Melbourne's outer northwest, on September 6, 2025.
Eight boys and young men, aged 15 to 19, have been charged with their murders.
The parents of one of the 16-year-old boys, who cannot be identified, objected to giving evidence at Melbourne Magistrates Court on Tuesday over concerns it would affect their relationship with their son.
But magistrate Stephen Ballek refused their formal objection, finding the nature of their evidence could outweigh any potential harm caused.
The boy's mother told the court she noticed her car seat was damaged on September 7 and believed her son had something sharp in his pocket.
He refused to hand it over so she instructed his father to ask about it when she dropped him off at his house for Father's Day, she told the court.
In his evidence, the father said he took his son to the back of the house where he embraced him and had a conversation.
He told the court he took the sword off the boy and placed it in his shed.
The man said he did not ask his son why he had the sword, nor about his alleged involvement in the Cobblebank murders.
The mother also denied asking her son questions.
Police seized the weapon from the father's property on September 19 and preliminary testing suggested it was likely the 16-year-old's DNA was on the sword's handle, the court was told.
It was also likely the DNA of one of the slain boys was on the blade.
Another three witnesses are expected to face Melbourne Magistrates Court on Wednesday after objecting to giving evidence over the alleged Cobblebank murders.
The three adult accused - Abel Sorzor, Prince Conteh, and Peter Addo - are due to return to court in May for a committal mention hearing.
The five other accused, all aged 15 and 16, will face a children's court at a later date.
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