Are blood money and expiation obligatory for someone who lent money to a woman for an abortion operation and accompanied her to the doctor, knowing that the woman later married and gave birth, and the age of the fetus was unknown?

As long as you have repented to Allah for your involvement in assisting the woman with the abortion, there is no blame upon you. A sincere repentance erases what came before it. You are not obligated to pay a blood-money (diyyah) or an expiation (kaffarah) for this abortion; rather, these are incumbent upon the one who directly performed the abortion.