Is it obligatory for you to fast as expiation for those who died in the second car, or is the expiation limited to your companion in your car?

If you were the cause of the accident, then you are liable for the blood money (Diyyah) of the deceased, and it is borne by the Aqilah (paternal relatives who pay blood money on behalf of a killer), as it is an accidental killing. You also owe two expiations for these two deceased individuals. Your loss of control over the car does not absolve you of responsibility, because the second collision resulted from the first, which occurred due to your negligence. The jurists have stipulated that if someone's horse bolted due to their own fault, they are liable for whatever it damages.