One of those men, Robert Davis, has appeared at an inquest into Mr Haines' 1988 death at Tamworth and declared the siblings' innocence.
Asked whether he and his brother, local boxer Eddie Davis, ever discussed the widespread rumours they had something to do with Mr Haines' death, Mr Davis said they didn't.
Mark Haines - pictured with his mother, sister and father - died from a traumatic head injury. (Supplied by Haines Family/AAP PHOTOS)
"We were innocent and there's no reason to discuss things," Robert Davis told the inquest at Tamworth court house on Tuesday.
"We didn't know him, I wasn't living in Tamworth and Eddie didn't know him either - he was only a kid.
"There was no reason for us to discuss it ... because we didn't do it."
The 17-year-old's body was found on the tracks south of the regional NSW city on the morning of January 16, 1988, not far from a crashed stolen car.
An autopsy showed the Gomeroi teenager died from a traumatic head injury.
The initial police investigation concluded he lay on the tracks either deliberately or in a dazed state, something his family has never believed.
The new inquest is examining the circumstances of Mr Haines' death and the original police investigation, after a campaign by his uncle Don Craigie to revisit the case.
Natalie Maher told the inquest she was with Mr Haines and his girlfriend Tanya White the night before his body was found, as a group of friends went to two nightclubs in Tamworth.
Ms Maher said she parted ways with the couple at the end of the night, only to hear about a body found on the tracks when she was woken by the 9am radio news on January 16.
The two women no longer speak because Ms White would not tell police what she knows about the night Mr Haines died, Ms Maher said.
Uncle Don Craigie campaigned for a new inquest to revisit Mark Haines' case. (HANDOUT/NSW GREENS)
"I've had frequent conversations over the years and (she's) stated she knows what happened to Mark and I begged her to tell police ... and she just will not," Ms Maher said.
"She said she's scared."
Ms Maher said Ms White had previously told her she knew who was in the car with Mr Haines that night, as well as who was driving.
However Ms Maher acknowledged she did not tell police about these revelations in her own statement to investigators in 2000, partly due to a sense of loyalty to her friend.
Through tears, Ms Maher said she remains haunted by Mr Haines' death and his emotional funeral.
"The sorrow, the grief, the wailing of the family ... how can you not speak up?
"These people were supposed to be his friends and I'm so sorry to Mark's family and I wish I could help more."
The inquest continues before Deputy State Coroner Harriet Grahame.
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