"I’m so grateful she and I got to reconnect and become such close friends before this tragedy,I will forever love you all.
"I’m now trying to help raise awareness about #violenceagainstwomen as monsters like this get away with this too often.
"I am also trying to raise money for my mum and dad who have given every little thing they own to help my sister try and get away from this monster.
"Woman and children should never have to suffer what they had to."
Mr Clarke's wife,Stacey Roberts,launcheda Facebook fundraising campaign on Wednesday to cover the four victims'funeral costs and help the Clarke family get through,what Nat Clarke described as,"the worst couple of weeks of our lives". It had raised more than $90,000 by Thursday afternoon.
Ms Clarke's father posted on social media that he believed his estranged son-in-law was rotting in hell and described him as a"monster"who only cared about himself.
"The scum rots in hell. If he truly loved them he would not have killed his children in such a horrible way,"Mr Clarke wrote.
"He might have said he cared[for] and loved his children,but I know it was always about him coming first."
Ms Clarke,31,died at the Royal Brisbane and Women's Hospital on Wednesday night after suffering severe burns when her car was set alight in Raven Street,Camp Hill in Brisbane's south-east.
Loading
Emergency services raced to the scene about 8.30am on Wednesday and neighbours tried to pull the victims from the burning car and use a garden hose to extinguish the flames.
Ms Clarke's three children – Laianah,Aaliyah and Trey aged between three and six - died in the car. Her estranged husband,Rowan Baxter,also died by suicide.
The couple reportedly separated late last year and were trying to work out custody arrangements. However,they were not involved in any proceedings in the Family Court or Federal Court.
Ms Clarke was a trampolining champion who represented Queensland for four consecutive years.
The couple's Integr8 fitness website described her as"an enthusiastic,passionate mother of three".
Loading
Kristy Watling posted on Facebook that she did not know Ms Clarke,but would see her nearly every day at school drop off.
"She was always smiling. I always admired her from afar. She was so fit and healthy,and her children were always so happy and well-behaved,"Ms Watling wrote.
"I just can’t get my head around anyone wanting to hurt them in such a horrendous way."
Another friend,Nicole Beeston,said she trained with Ms Clarke and vowed to"forever remember"the mother and her"beautiful kids".
"Today I drove the way I use to go when we trained together,"Ms Beeston wrote.
"Instead of laughing and training all those years ago,I laid flowers and a Crossfit shirt with you and the kids'name on it.
"You and your babies'legacy will live on. I will paddleboard this weekend thinking of you and the kids."
If you or someone you know needs help,support is available at Lifeline on 13 11 14,Beyondblue on 1300 224 636,or 1800 RESPECT.