Sgt. DB Gates says the 40-year-old son-in-law of the driver died Monday.
Authorities say a 68-year-old woman was in a Jeep SUV with her 3-year-old grandson when the vehicle crashed through the house on Friday, injuring a 70-year-old man who was her partner, her son-in-law and her 34-year-old daughter.
The 70-year-old man died at the home. The daughter remains hospitalized at Harborview Medical Center. The grandson was not injured.
Gates says the woman is being investigated for vehicular homicide, but has been released from county jail.
Authorities say the car plowed through a room in the home, then onto the deck and dock.