Alfer Azzopardi, Michael Baltatzis and Sean Gabriel were aged 19 at the time of crime and one of their victims was the former president of Australian Medical Association Dr Mukesh Haikerwal in September 2008.

A Melbourne based court today agreed that the original sentence had involved some double punishment.

"It is impermissible for an offender to be punished twice for the same act," Justice Robert Redlich said.

He said six counts involved double punishment and this would allow an appeal.

In the County Court in November 2009, Judge Joe Gullaci jailed Azzopardi for 18-and-a-half years with a minimum of 13-and-a-half years, Baltatzis for 16-and-a-half years with a 10-and-a-half year minimum and Gabriel for nine years and nine months with a minimum of six years.

However, Justice Redlich said Judge Gullaci had "failed to give sufficient weight to the youth of each applicant."

Their youth, though subjugated to other punitive sentencing considerations, remained a relevant mitigating circumstance requiring some degree of leniency that would not be extended to a mature offender.

"The orders for cumulation and their aggregation failed to adequately reflect the applicants' youth and their prospects for rehabilitation."

Justice Redlich said the total sentences exceeded what was necessary to achieve all relevant sentencing objectives. He slashed their sentences by up to four-and-a-half years each.

Azzopardi's sentence is now 16 years, with a minimum of 10-and-a-half years, while Baltatzis' is now 12 years with a minimum of seven. Gabriel's sentence is now seven years with a minimum of four years.

The trio pointed a knife at Haikerwal and demanded his phone and wallet. He was hit up to 12 times with a baseball bat. Part of Haikerwal's brain was removed in surgery following the assault.

There were 34 victims in 21 separate incidents on 11 different evenings.

Azzopardi and Baltatzis pleaded guilty to 46 charges each, and Gabriel, who was only involved in the offending on one night, pleaded guilty to 10 counts.