Crown prosecutor Sharn Coombes told the Supreme Court on Monday that Georgia Fields, 19, and Jake Fairest, 26, who are on bail, had been assessed and found to be unfit to stand trial. A third man, Warwick Toohey, 37, who appeared via video link from prison, needed further assessment.

Justice Lex Lasry reserved any decision as to whether the trio's trial would proceed until next year.

A trial date had been set down for May 2, but Justice Lasry adjourned the case to February 8, when a directions hearing will be held to get an update on the fitness to plead question for the trio.

Ms Fields, Mr Toohey and Mr Fairest are charged with murdering Robbie Wright, who fell from a balcony outside his Ringwood apartment on January 15. Mr Wright, 36, who also suffered from cerebral palsy and epilepsy, and had an intellectual disability, died in hospital three days later.

Ms Fields is profoundly deaf and can communicate only by sign language and in writing.

Mr Fairest has severe cognitive and developmental disabilities caused by aggressive chemotherapy treatment to a brain tumour when he was seven. The treatment also caused stunted growth, a weakened spine and a growth hormone deficiency.

Previous court hearings have been told Mr Wright and Mr Toohey lived together but were constantly arguing over household tasks. Both men had allegedly previously "shared" Ms Fields as a girlfriend.

The trio allegedly confronted Mr Wright in his lounge room, restrained him and forced him out on to the balcony and over the hand rail.

CCTV footage of the trio using Auslan sign language on a train to Ringwood, in the foyer of Mr Wright's apartment and in the lift on the way to confront him, formed part of the Crown case against them because the recordings suggested they had allegedly been planning the murder.

An Auslan interpreter had analysed the CCTV footage to provide a transcript of what the trio had been saying in the lead-up to Mr Wright's death.

The interpreter could not identify some parts of the conversation because the trio at times were using slang terms.

When they entered the foyer at 9.40pm and took the lift to the second floor, the CCTV footage allegedly showed Ms Fields asking Mr Fairest in sign language if he wanted Mr Wright dead or alive and asking the question, "How die?"

The alleged conversation included Mr Fairest saying: "Want strangle."

Ms Fields: "Fall."

Mr Fairest: "Can strangle neck area. What do you think?"

Ms Fields: "I think falling is better."

Mr Toohey: "Strangle risky."

Ms Fields: "Fall good, fall good."

Mr Toohey then allegedly told Fairest: "You grab, hold."

Ms Fields then allegedly replied: "Fall good, all right."

Mr Toohey then allegedly told Mr Fairest to greet Mr Wright and to "grab and to push forward".