We understand your concern for your younger brother and his spiritual journey. It's important to remember that Jesus said "Everyone therefore who confesses me before men, him I will also confess before my Father who is in heaven. But whoever denies me before men, him I will also deny before my Father who is in heaven" Matthew 10:32-33 WEB.
Your brother's avoidance of discussions about Jesus, His resurrection, or the Nativity may indicate that he is not truly born again or dealing with some spiritual confusion or conflict. It's crucial to remember that salvation comes only through faith in Jesus Christ, as the Bible tells us, "because if you will confess with your mouth that Jesus is Lord, and believe in your heart that God raised him from the dead, you will be saved. For with the heart, one believes resulting in righteousness; and with the mouth confession is made resulting in salvation. For the Scripture says, 'Whoever believes in him will not be disappointed'" Romans 10:9-11 WEB. We pray in Jesus name because "For there is one God, and one mediator between God and men, the man Christ Jesus" 1 Timothy 2:5.
Let us pray together for your brother. "Lord Jesus, we lift up our brother who has strayed from openly confessing Your name. We pray that the Holy Spirit would convict him and draw him back to You. Help him see and testify to the truth of Your resurrection and Your glory. We agree together that he would be strong and acknowledge you before men as the Lord God and grow before God. We wholeheartedly ask this in Your precious name, Jesus. Amen."
We encourage you to continue praying for him and to share testimonies with him whenever appropriate. Be open and share the Gospel with him as it's clear he needs to understand the truth. And this is his only hope, it may seem harsh but "For no other foundation can anyone lay than that which is laid, which is Jesus Christ. If anyone builds on this foundation gold, silver, precious stones, wood, hay, or straw, each man's work will be revealed. For the Day will declare it, because it is revealed in fire; and the fire itself will test what sort of work each man's work is" 1 Corinthians 3:11-13 WEB. Be encouraged too, as you have shown concern for your brother's faith and eternal life, God also promises us, "The Lord is not slow concerning His promise, as some count slowness; but is patient with us, not wishing that any should perish, but that all should come to repentance" 2 Peter 3:9 WEB. Continue to trust in the Lord and stand strong in your faith, and be encouraged knowing that God is able and willing to save your brother.