Marcus Rappel, who is serving a 23-year jail sentence for murdering his partner Tara Costigan, was the only one not legally represented when he appeared in the ACT Magistrates Court on Thursday.

When his name was called, he turned around and made an obscene gesture at members of the media sitting in the public gallery.

He pleaded not guilty to the alleged bashing.

He told Special Magistrate Ken Cush that he had separated from his lawyer but he would "try to rustle" one up before the next hearing date.

Rappel, 43, and fellow detainees Daniel Grech, 28, Alex Bourne, 30, and Jeremy Reid, 26, are each charged with recklessly inflicting grievous bodily harm on one brother, and assault causing actual bodily harm on the other.

Isileli Paea Taholo, 31, who is charged with aiding and abetting the four to assault one brother, and assaulting the other, pleaded not guilty to the alleged offences last month.

He is currently in immigration detention.

The five men are accused of bashing the two brothers in their cells in the Alexander Maconochie Centre on August 7.

Both men were taken to hospital.

One was returned to jail the same day, while the other was admitted to hospital and returned to prison the next evening.

Corrections Minister Shane Rattenbury said at the time there was "extensive CCTV footage of this incident".

All five are due back in court on March 29.