Police said the victims were the children of the suspect's girlfriend.
Police were called to a home on E. 86th St. in Garfield Heights around 9:30 p.m. Wednesday.
When officers arrived they found two victims in the driveway.
A 17-year-old boy was taken to Marymount Hospital where he was pronounced dead. His 19-year-old sister was transported to MetroHealth Medical Center where she underwent surgery but died of her injuries.
Police said the 29-year-old suspect barricaded himself in the house following the shooting.
"One of our officers is a crisis intervention officer," Chief Robert Byrne, Garfield Heights police, said. "He immediately made contact with him on the cell phone and talked to him along with the suspect's mother."
"There were in a three way conversation and talked to him and whole time and ultimately came out peacefully," Byrne said.
The standoff ended after about four hours.
"This initially stems from a domestic disturbance," Byrne said. "We're in the early stages of the investigation at this point."
He said the suspect was fighting with his girlfriend. She was taken to Marymount Hospital for treatment of minor injuries.
Police said the suspect, who has not been identified, was arrested for aggravated murder and other charges.
The names of the victims were not released.
A neighbor said she was at a nearby convenience store when she heard about 20 shots.
"When we came home the street was blocked off and they said they had two kids laying in a driveway," Tina Lassiter said.
"It's pretty crazy because I just lost my brother a year ago on Grand Division [Avenue] and ever since then we've had nothing but problems over here," she said.