The man hailed a hero for tackling one of the gunmen who killed 15 people at Bondi Beach has pleaded not guilty to allegedly assaulting his father, a Sydney court has heard.

Ahmed al Ahmed, 44, appeared before Bankstown Local Court on Wednesday to face charges of assault as well as stalking and intimidation in relation to an incident in March.

Outside court, Ahmed’s lawyer said the case has been “very difficult” for his client and it is a “family situation he never expected”.

On 14 December, Ahmed jumped on Sajid Akram from behind as he opened fire on a crowd at a Jewish event, wrestling a long-arm gun from the gunman. A second alleged gunman shot Ahmed several times in the arm.

The attack was Australia’s deadliest mass shooting since 1996 with police declaring it a terrorist incident that had targeted the Jewish community.

Video footage of Ahmed’s actions received international coverage, prompting a fundraiser that collected more than A$2.5m (£1.24m; $1.7m) for him.

After he was charged earlier this month, Ahmed told local media that the claims of assault were “not true at all”.

In a separate matter, two of Ahmed’s brothers have recently been charged over allegations they threatened him and tried to extort some of the donations he had received.

Hozifa al Ahmed and Sameh al Ahmed moved to Australia after the shooting and lived with Ahmed, but their relationship broke down. It is alleged that the two brothers threatened to hurt Ahmed if he did not hand over $100,000 to each of them.

As he left the court on Wednesday, Ahmed replied “no comment” when asked if his family was lying and if he thinks he can make peace with his father and brothers.

In the days after the Bondi Beach shooting, Australia’s Prime Minister Anthony Albanese visited Ahmed as he recovered in hospital, calling him “the best of our country”.

In a TV interview, Ahmed – who was born and raised in Syria – described the moments before he tackled the gunman, saying he wanted to stop innocent people being killed and that “my soul” was “asking me to do that”.

The case is due back in court in August, with a hearing set for December.