What is the expiation for having intercourse with a girl before the completion of marriage and the contract, which led to pregnancy and its abortion out of fear of the family?

You both committed grave transgressions such as fornication and abortion. Abortion is forbidden, even if the fetus is in the nuṭfah stage, according to the preponderant opinion. You both must repent from fornication, and whoever directly performed the abortion or assisted in it must also repent.