What should I do concerning expiation for killing if I am unable to fast and the victim's family has pardoned me?

There are two consequences for accidental killing: blood money (Diyah) to be paid by the killer's 'Aqilah (male relatives on the paternal side) (unless the victim's guardians forgive it), and expiation (Kaffarah (definition)).

The expiation involves freeing a believing slave; if one cannot be found, then fasting for two consecutive months.

Allah the Almighty says: "And never is it for a believer to kill a believer except by mistake. And whoever kills a believer by mistake – then the freeing of a believing slave and a compensation payment presented to his family, unless they remit it as charity. But if he was from a people hostile to you and he was a believer – then the freeing of a believing slave. And if he was from a people with whom you have a treaty – then a compensation payment presented to his family and the freeing of a believing slave. And he who does not find [a slave] – then a fast for two consecutive months as repentance to Allah. And ever is Allah Knowing and Wise." (An-Nisa: 92).

According to the majority of scholars, feeding sixty poor people is not part of the expiation for killing; rather, it is primarily by freeing a slave, and if that is not possible, then by fasting for two consecutive months.

If the victim's family forgives the blood money, then what is obligatory is the expiation. And since freeing a slave is impossible due to the absence of slaves, then fasting becomes incumbent upon you.

Enduring the performance of fasting, as long as you are able to do so, is better for you.