My son is 18 and living at home and my daughter is 20 living at home. Do I need to insurance them or just the vehicles? 
An auto policy insures an automobile . The automobile is registered to at least one member of a household . The entire household is insured while operating that vehicle . You can exclude a poor driver . If excluded the driver can not operate any vehicle registered to the household . If a covered driver operates an auto that is not registered to the household , coverage is extended in the event the loss in an accident exceeds the limits of the policy covering that vehicle . 