My lawyer told me that no court order is meant to place children in danger. If you believe based on what you know about the accident that your ex poses a danger to the kids, no one will fault you for keeping them with you.
If you have disturbing information from the police and no information from him, you have to make the best decision possible with the information available to you at the time. It sounds like that means keeping the kids with you.
If you want to pm me, I can share the supervision plan in my court order (basically a series of "steps" that ex has to complete in order to get less restricted time with Kid - if he fails SoberLink or has an "alcohol related incident", he falls back a "step").