Police say Andrew Austin came home about 5 p.m. Monday to find his two stepchildren, 16-year-old Kaitlin Austin and 12-year-old Ethan Austin, dead of apparent gunshot wounds.
Andrew Austin is the boy's biological father and the girl's stepfather.
Sgt. Ken Lattin with Kennewick Police says it appears that at least one victim had multiple gunshot wounds. A handgun was found at the scene.
An autopsy is scheduled for both on Wednesday.
Investigators continue to canvass the neighborhood, looking for anyone who may have seen or heard what happened. The officer says it doesn't appear that anyone broke into the house.
Investigators say four people were living in the house, the two children and the mother and father.