Only God knows your brother's true spiritual state, and whether or not he's resisted God for so long that he can no longer hear God's call. But don't give up praying for him, because God is still able to break through his rebellion and convict him of his need of Christ.
At the same time, the Bible does warn us about the dangers of repeated spiritual rebellion. Have you ever worked in your garden or at some other task for so long that your hands grew hard and calloused? When that happens, our hands aren't as sensitive as they once were, and we can't feel the things we once felt.
The same thing can happen to our hearts. When we repeatedly turn away from God and refuse to listen to Him, slowly but surely our souls grow hard and calloused, and we can no longer hear God's call the way we once did. The Bible warns, "A man who remains stiff-necked after many rebukes will suddenly be destroyed -- without remedy" (Proverbs 29:1). The Bible also says, "Today, if you hear his voice, do not harden your hearts" (Hebrews 4:7).
Let your brother know of your concern for him. Don't argue with him; it will only cause him to be even more rebellious. Confront him also with the possibility that his rebellion against God is actually a result of his rebellion against your parents. But it shouldn't be this way. God still loves him and yearns for him to be part of His family forever.