Family members of Scott Guy called as key witnesses in the Ewen Macdonald murder trial are being monitored closely by Victim Support, as they face the unusual stress of being called time after time to the witness stand over the six-week hearing.

Four close relatives of the slain farmer's immediate family are each giving evidence up to five times as the jury in the High Court trial hears evidence chronologically.

"It means they are not able to be in the courtroom until they have delivered their evidence. That places some emotional challenges on them," said Victim Support CEO Tony Pain.

The high-profile trial of father-of-four Macdonald, 32, started this week at the High Court in Wellington. This week will focus on the relationship between him and Guy - crucial to establishing a motive.

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The Crown alleges Macdonald shot and killed Guy, his 31-year-old brother-in-law, early on July 8, 2010, after growing tensions over the future of the family farm they co-managed.

The four key witnesses are Scott Guy's father Bryan, wife Kylee Guy, sister Nikki Guy, and other sister Anna - who is Macdonald's wife.

Macdonald has avoided eye contact with his closest family members so far.

Dr Chris Gallavin, from Canterbury University law school, said delivering a case in chronological order was quite rare. "This case will be particularly traumatic for the family as, of course, the family of the victim is also the family of the accused."

Auckland University law professor Warren Brookbanks says giving evidence multiple times is particularly harsh.

"It's not something one would want to happen, but sometimes those things are unavoidable in a criminal trial."

The trial before Justice France and a jury of 11 resumes tomorrow.