What is the expiation for shared accidental killing?

Question:
My son was involved in an accident with his companion, and the passenger passed away...?

Answer:
If it was due to his actions, he must fast two consecutive months.
Q: And if the mistake was on both of them?
A: Each of them owes two months.
Q: But my son’s health condition does not allow him to fast?
A: If he is able... it remains a debt on him until it becomes easy for him. There is nothing else but freeing a slave, and freeing a slave is not feasible.