He's going to feel extreamly bad when he wakes up. This can be a good thing. It is an event that can prompt a radical change in behavior.
He wasn't caught at a "roadblock." He wasn't public intox. The objective evidence is clear--he could have caused a major accident. He could have harmed another person. This will probably come home to him in a strong way.
Do whatever it takes to try to prevent job loss (he will be able to get work driving priviladges in 3 weeks or so) and get the car out of impound ASAP (daily fees willl build up rapidly). Your family finances are very important.
Follow the law 100%---he is forbidden to drive, period.
The need for a lawyer depends upon the offense (is this the first DUI?) and possiable penalities. He will be facing at least some mandatory incarceration (from 3 days to significantly longer, depending on juristiction). Cross each bridge as you come to it, do not become overwhelmed with the big picture. Give him same advise.
As I said, he's gonna feel bad about this. Don't put personal anger on top of the problem, but beyond the above and getting him to court, don't ease the consequences of his actions. Expect him to deal with this as an adult, to come to adult conclusions, and to do the right thing.
If he chooses to make it so, this could be a turning point that improves his life and yours. If he fails to respond effectivly, this could be the beginning of the end. It's up to him. I hope he sees that.