You are a warner, not a miracle machine.
Every people gets a guide; results belong to Allah
Ibn Kathir notes that the idolaters asked the Prophet ﷺ to turn the hill of Safa into gold and move the mountains away. The reply: you are only a warner. Guidance is not your burden, and every people has had someone calling them.
Your brother stopped praying and you have sent him every reminder clip there is. You lie awake running the next argument. Your part is to say it well and with love. The heart is not in your hands.
If they do not change, it means I did not find the right words.
My job is to convey kindly. Changing hearts is Allah's.
Think of the person you most want to guide. Make dua for them instead of planning your next argument.