Mr Wright would have been unable to defend himself when he was thrown off a Ringwood balcony in 2015 because of his cerebral palsy and reduced functionality in his left leg, the Victorian Supreme Court heard on Friday.
"The terror he must have felt, hanging on to the side of the balcony until he could hang on no longer," his sister Leanne Power told the court.
"I've lost count of the sleepless nights spent thinking about his last moments."
Jake Fairest, Georgia Fields and her ex-boyfriend Warwick Toohey were found unfit to stand trial over Mr Wright's murder.
Toohey (30) and Fairest (27) are intellectually disabled while 20-year-old Fields suffers from atypical autism and has low intelligence.
All three are profoundly deaf, as was their victim, who also had epilepsy.
Mr Wright's sister is worried his autistic and intellectually disabled killers will be allowed to avoid custody because of their special needs.
"What message does this send to the community - 'if I have a a disability, I can get away with things'?" Ms Power said.
"I believe that jail is the best option for them."
Her father believes Fairest and Fields will commit a similar crime unless they are incarcerated.
"They have to be shown that their conduct is not acceptable in our society, and therefore should lose their freedom," Joseph Wright said in a statement read by prosecutor Christopher Dane QC.
In October, a jury in a special hearing found the trio had murdered Mr Wright in January 2015 by throwing the 36-year-old off the balcony of the Ringwood unit he shared with Toohey.
The finding sparked an unprecedented legal conundrum as the court, the prosecution and separate defence lawyers considered whether the trio should be subject to custodial or non-custodial supervision.
Fairest and Fields, who are free on bail, returned to court on Friday for a further hearing about their future.
Toohey was given an indefinite custodial supervision order in February for his part in Mr Wright's murder and will spend at least 25 years at a residential facility overseen by the Department of Health and Human Services.
Fairest, Fields and Toohey were captured on camera telling each other through sign language it would be "easy" to make Mr Wright fall to his death and "splatter".
Mr Wright fell 12 metres about half-an-hour after the murder plot was captured by CCTV cameras on a Ringwood-bound train on January 15, 2015.
The trio killed Mr Wright because they wanted his unit for themselves.
Mr Wright's father said they murdered a defenceless man and threw him off the balcony "like a dead piece of meat".
"He was not able to defend himself against the murderous onslaught," Joseph Wright said.
"I cannot imagine the dreadful terror he must have felt in that terrible moment."
The matter will return to court on Monday.
