They plan to protest near a former family home, under which lies a well they believe holds the remains of Maureen Braddy and Allan Whyte.

Family members have renewed calls for Victoria Police to investigate the well which they believe could hold evidence of the teenagers' fate.

Maureen and Allan went missing on November 23, 1968. Decades later a coroner ruled foul play was most likely involved in their disappearance, but there was not enough evidence to lay charges.

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Family members have long believed the well is among two sites that might reveal what happened to Maureen and Allan.

But authorities say there is not enough evidence to justify digging up the well, which now sits under the loungeroom of a weatherboard home.

Maureen's sister Lyn Butterworth said a search of the well would bring closure to the families.

Mrs Butterworth said everything pointed to Maureen and Allan being buried in the well, saying she did not even consider the possibility it would be empty.

She said there was no hope her father Stan Braddy - suspected of murdering the pair - would ever stand trial, as he was in his 90s with dementia.

Mr Braddy told a 2012 inquest he was confident the pair were still alive. He said he believed Maureen and Allan were abducted as part of a "slavery trade arrangement".

Mrs Butterworth said she just couldn't understand why the well had never been investigated.

At the 2012 inquest into Maureen and Allan's death, Mrs Butterworth testified that she saw her father and one of his friends "holding something" which was "covered with blood".

Mrs Butterworth told the Bendigo Advertiser it would mean the world to have the site investigated.

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"Once we've got that well dug up, that's all we ask, and I'll just walk away, I won't push," she said.

"The police can deal with whatever happens afterwards, we just want the well dug up."

Victoria Police told the Bendigo Advertiser in April that the investigation into Maureen and Allan's deaths remained ongoing.

They encouraged anyone with information to come forward.

They said police assessed, and if validated, actioned any information they received.

The rally will take place on Saturday.

Mrs Butterworth requested attendees didn't park in the area, so traffic could get in and out.

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