Their mother, Mitchelle Blair, arrested and charged has confessed.
The family told FOX 2 that every time they tried to contact one of the two kids, including Stoni Ann Blair (seen in a photo with her father), all they received were excuses as to why they couldn't.
They believe that all four of Blair's children had been abused for years.
Tracy Dorsey, went to Detroit Central High School, in the same class as Blair, the mother of Stoni, then 13 - who would now be 15 years old - and her brother, Stephen Blair, 11, who was 9 years old at the time of death.
Tracy is also Stoni's aunt and is the sister of her father Alexander Dorsey.
She said she does not know about Blair's mental state leading her to such an act.
"I do not know," Dorsey. "I do not know where her mind is."
She praised Alexander as a father.
"He's a great father," she said. "He wanted his kids, she just wouldn't give them to him. The fight wasn't probably in him to go."
FOX 2: "Did he have a relationship with Michelle?"
"No," Dorsey said. "Not since they broke up years and years ago. No. Because she was always trying to pick arguments and just wanted money from him.
"She just wanted money."
Other family members said that Stoni's father was prevented from trying to see her. Alexander had not seen her in about a year.
"She would threaten to call the police," said Linda Dorsey, Stoni's grandmother. "Saying he was trying to break into the house. Or saying that he had done something to her. Not the kids, but her.
"I don't know how my other babies were able to stay there, knowing that it's going on. But I figure that had to be fear."
Stoni's cousin Biranna Dorsey also spoke to FOX 2.
"It makes me angry," she said. "That's it. Just angry, It hurt that she can do that."