The actions of Rowan Baxter on February 19, 2020, in suburban Brisbane caused the deaths of Ms Clarke as well as Aaliyah, six, Laianah, four, and Trey, three.
Baxter was a short-tempered hothead, who was paranoid and controlling and treated his wife and children as possessions, the inquest sitting in Brisbane was told on Wednesday.
Lewis Bartlett, who knew Baxter from about 2008 and employed Ms Clarke at his sports shoe store, told the inquest she confided about intending to leave her husband late in 2019.
"I was shocked at the time because on the surface they looked like a happy couple," Mr Bartlett said.
Ms Clarke later told him she and Baxter had what was "classed as a domestic violence relationship".
She said he had not hit her, but "had done other things" that she did not elaborate on.
Mr Bartlett said Ms Clarke told him that she could not do anything without Baxter's permission, and her husband wouldn't let her wear shorts to work even though it was allowed at the store.
In the weeks before the 31-year-old and her three children were killed, Ms Clarke asked Mr Bartlett how to write a will.
"She said if anything ever happened to her she wanted to make sure her children were well looked after and went to the right people," Mr Bartlett told the inquest.
When he replied that nothing would happen to her, Ms Clarke said: "No, he's going to try and kill me."
"She was convinced something was going to happen," Mr Bartlett said.
Ms Clarke said she had told the police her concerns and he thought things would be put in place to protect her.
Mr Bartlett said Ms Clarke had fears about what Baxter would do to her, but didn't think he would harm the children.
"But she did say that he would use the kids against her as almost like a bargaining chip," he said.
Ms Clarke also told Mr Bartlett that Baxter grabbed her arm, assaulting her, when he dropped off the children after their separation on January 31.
"She said ... she went to get the kids out the car and saw these photos of herself in her underwear on the back seat," Mr Bartlett said.
Ms Clarke went to grab the photos so Baxter wouldn't have them and he grabbed her arm, holding her up against the car.
Ms Clarke also told friends she thought Baxter was stalking her and had bugged her phone or was somehow listening to her conversations.
Baxter, 42, was also injured in the car fire, but died nearby after stabbing himself.
Ms Clarke died later the same day in hospital.
The inquest continues.
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