He had previously pleaded not guilty to the four charges, but changed his plea Friday.
Ralphael was pronounced dead at the scene and Estella died from injuries at Greene Memorial Hospital, according to Xenia police.
A witness reported the deadly attack to 911 dispatchers.
“My friend stabbed his mom,” the caller told 911 dispatchers. “She’s laying here on the floor. She needs an ambulance...There’s blood everywhere.”
While the witness was on the phone with dispatchers, Winston also called 911.
“My mom and my sister got into an argument and I stabbed them,” he said.
Once in custody, Winston told detectives that there was “no excuse” for what he did, according to court documents.
The witness told police that everyone was getting ready to eat dinner when Winston began arguing with his mother, according to a police report.
During the argument, Winston grabbed a knife and stabbed Estella.
He continued arguing with Ralphael and stabbed her also, according to records.
The knife was found at the scene.
Winston had been living at the Hardacre Drive home with his mother, sister and father since August 2018, according to court documents.
His father reportedly died recently.