Jeffrey Flores, 25, of Pinole, was arrested at the scene in connection to the two homicides, according to police. The man and woman found dead, who are in their 50s or older, were relatives of Flores. Their names have not yet been released.
A woman who is believed to be Flores' sister was also at the home when officers arrived on the scene, along with three children under 10 years old.
It is unknown how Flores is related to the victims, police said.
Officers responded to the 1100 block of Tara Hills Drive for an unknown problem around 2:30 a.m., police said Saturday.
Officers arrived at the two-story home and spoke to a resident who said there might be injured people inside, police said.
Police served a search warrant at the home later in the morning and were collecting evidence a short time after noon. Inside, the officers found the deceased man and woman, police said.
While an investigation is ongoing, police said this appears to be an isolated incident and all persons of interest are in custody.
Flores was booked into the Martinez Detention Facility on suspicion of two homicides, and is being held in lieu of $2 million bail. The killings are Pinole's first homicides this year and are believed to be the first murders in the city since 2011.
Anyone with information about the case is asked to call Pinole police at (510) 724-8950.