His brother, Soh Wee Kian, 25, is serving a life sentence for stabbing a woman to death in 2010.
Their stepfather, Ng Chee Yong, 46, is also behind bars for drug-related offences.
Yesterday, Soh Wee Boon, 22, was jailed for four months after pleading guilty to one count each of criminal intimidation and insulting a woman's modesty.
The 24-year-old woman was walking home at around 9pm on Dec 16 last year when Soh approached her and told her about his family background.
He then tried to sell her packets of tissue paper.
When she declined to buy them, he took her to a corner of the void deck of a block of flats in Woodlands.
He then told her he had a penknife and ordered her not to shout or call the police.
While talking to her, Soh started fondling his private parts through his shorts.
The woman, who is not named to protect her identity, felt insulted by what she saw and walked away, the court heard. She notified the police about an hour later.
Soh's lawyer, Mr Ng Shi Yang, said in mitigation that his client had a "troubled and complicated family background".
"He has had to fend for himself and his family ever since he left school in Secondary 2, with no one else to take care of his mother and nine-year-old half-sister," Mr Ng said.
For criminal intimidation, Soh could have been jailed up to two years and fined.
For insulting a woman's modesty, he could have been jailed up to a year and fined.
This article was first published on August 1, 2015. Get The New Paper for more stories.