What must a man who twice committed indecency with his fiancée, resulting in two abortions, then married her and she aborted two more times, do to atone for his sin?

The fiancée, before the legal marriage contract, is a stranger (non-mahram). Committing fornication with her is a grave indecency, as Allah Almighty says: {And do not approach unlawful sexual intercourse. Indeed, it is ever an indecency and is evil as a way.} (17:32). If, in addition to that, the fetus is aborted, the crime becomes even greater. The perpetrator must offer sincere repentance. Whoever participated in the abortion after the formation of the fetus must pay a ghura (a male or female slave, or its value), and if that is not found, then one-tenth of the mother's blood money. There is a difference of opinion regarding the obligation of expiation by fasting for two consecutive months.