Who would/could be sued if an accident resulted in lost lives caused by driver authorized on vehicle owner's auto insurance?

In general you can only sue the driver of the at fault vehicle.  But if the driver was working for the owner of the vehicle or was doing an errand for the owner of the vehicle, then you can also sue the owner of the vehicle.  In addition, if the owner of the vehicle negligently entrusted the vehicle to the driver, then you can also sue the owner of the vehicle.  Good luck with this matter.