Is expiation (kaffarah) obligatory for someone who unintentionally caused the death of two people as a result of a car accident?

If what happened was beyond your control, and there was no negligence or dereliction on your part, then nothing is required of you. However, if the accident was due to your error, negligence, or dereliction, then you are obliged to offer expiation (kaffarah) and pay blood money (diyah), and you do not inherit from your mother's diyah — if it becomes obligatory. Scholars have differed regarding inheritance from her estate.