Prosecutors said in court documents that Mark Mullan's preliminary blood-alcohol level was 0.22 after Monday's crash. Washington's legal limit for driving of .08.
Mullan, 50, remains jailed on $2.5 million bail, with arraignment scheduled for April 11. It's not known if he has a lawyer.
He faces a sentencing range of 15 to 19 years in prison if he's convicted as charged.
The crash killed Dennis and Judith Schulte, retired teachers from Kokomo, Ind., who recently moved to Seattle.
Thirty-three-year-old Karina Schulte and her infant son, Elias, were critically injured.
In court papers, prosecutors said Monday was the first day Karina Schulte had ventured out for a walk since the recent birth of her son and the first day her husband, Daniel Schulte, had returned to work.
Mullan's truck was traveling at 30-40 mph and didn't slow or take evasive action as the three adults, with the baby carried by his mother in a sling, legally crossed a neighborhood street at an intersection, prosecutors said.
The infant, initially found not breathing, suffered multiple skull fractures and brain injury and has undergone emergency surgery for liver and intestinal injury, court documents said.
His mother suffered a crushed pelvis. She also developed blood clots due to her injuries and suffered a stroke that has led to brain damage, prosecutors said.
At the time of the crash, Mullan was on probation for a DUI conviction in January for an incident that occurred on Christmas Day. Conditions of his probation included that he not use alcohol and not drive without a valid license and an ignition interlock device.
Prosecutors said he was driving with neither a valid license nor ignition interlock. He has another DUI charge pending trial in Snohomish County.
Mullan's history includes two 1990 DUI convictions in Puyallup in Pierce County and a 1994 DUI deferred prosecution that was dismissed in 1998, prosecutors said.
"Mr. Mullan is a grave danger to the community who cannot or will not refrain from driving impaired," Senior Deputy Prosecutor Amy Freedheim wrote in a court statement requesting bail be maintained at $2.5 million.