You know that and have confessed your sin. God has forgiven you. Jesus is the proof of his mercy. Without repentance which includes faith in Jesus for forgiveness, your half brother is still under the curse of the law of God because of his sin. All sins, even the sin of abortion and the cover-up are forgiven by God through Jesus Christ, crucified and arisen.
Abortion is never an acceptable alternative.
I am happy that your marriage and life is better now that the cover-up is over. It is sad that your half-brother continues not to tell the truth. You are right to keep him in your prayers that he will repent. We are happy to hear that you talked to your pastor and that you have heard absolution from him. We are also happy to share your warning with others.