Police have charged two men aged 18 and 20 with murder over the stabbing death of Peter Hofmann.

The bus driver was found dead in his car in Sydney's eastern beaches on June 21.

An investigation was launched into the circumstances of the Maroubra murder, as the 68-year-old's sister appealed to the public for answers.

Patricia Hofmann said her brother was homeless at the time of his death and he was a quiet and gentle man who did not deserve to die.

She said Mr Hoffman fell victim of a scam which left him without a roof over his head, and he had politely refused offers for help.

Both men have been refused bail and will appear in Waverley Local Court on Friday.