The federal government has provided heavily redacted documents to lawyers representing a Tamil family detained on Christmas Island, entirely blacking out details of discussions between Australian and Sri Lankan authorities on the matter.

In a pre-hearing before Melbourne’s federal court on Monday, lawyers representing the family, known as the Bileola family after the Queensland town where they had been living, said they had also been given a redacted document about a ministry briefing between the home affairs minister Peter Dutton and the department secretary.

The documents had been received late on Sunday night but could prove “critical” to the case when it is heard on Friday, lawyer Angel Aleksov said, who is representing Priya and Nades and their Australian-born daughters Kopika and Tharunicaa.

Justice Mark Moshinsky agreed “it does look like there has been some overenthusiasm for redaction” by the government, and questioned why even the surname of someone from the department had been redacted.

“Of course if there are confidentiality issues they can be dealt with in a different way that doesn’t require redaction,” Moshinsky said. “I was having a little trouble piecing who was who together because of the surnames being redacted.”

Moshinsky said the government should provide the non-redacted documents to Aleksov, and that the hearing would recommence at 3pm Monday if the redaction issue had not been resolved by then.

It was not resolved, and when the case recommenced, Jonathan Barrington, representing the minister, requested the redacted information be protected because it related to foreign relations.

Mochinsky read the unredacted documents and said he was inclined to agree, but reserved his final ruling until the hearing in case the redacted matters become relevant.

The case is expected to take one day when it is heard on Friday, and there will be no cross-examination of witnesses, the court heard.