What can be done to atone for the sin of a father who killed unintentionally and did not atone for his sin before his death, due to his ignorance of the ruling?

In cases of accidental killing, two things become obligatory: a financial right, which is the blood money (diyya) paid by the killer's 'aqila (male agnates) to the victim's family, unless they pardon it; and an expiatory right (kaffara), which is the freeing of a believing slave. If one cannot find a slave to free, then it is fasting for two consecutive months. The diyya is on the 'aqila, as agreed upon by scholars. The kaffara is from the killer's own money, and no one shares in bearing its cost. If the killer leaves no money, then it is recommended for his children to feed (the poor) on his behalf.