Yes, I have; in fact, almost every day I get at least one letter from someone who has been dramatically changed because they've given their life to Christ.
You see, when we sincerely commit our lives to Jesus Christ, God Himself comes to live within us by His Holy Spirit. Our sins are forgiven, and God puts our feet on a new path–His path. He also gives us a new purpose in life: to live for Him and not for ourselves. The Bible says, "Therefore, if anyone is in Christ, he is a new creation; the old has gone, the new has come! All this is from God" (2 Corinthians 5:17-18).
Only God knows your brother's heart–but I hope you will encourage him and do all you can to help him. For most of his life, your brother has been on a dead-end road–but with Christ in his heart, his life can be different. Ask him to tell you more about his commitment to Christ, and urge him to get connected with other Christians. Urge him also to make the Bible, which is God's Word, the foundation and guide of his life.
Perhaps the reason you doubt if your brother can really change is because you haven't experienced Christ's transforming power in your own life. You may not be in the same situation he is–but you need your sins to be forgiven also, and you need Christ's hope and guidance every day. Commit your life to Him today.