They ask me to fix my drifting sibling

I taught for forty years in Bursa and thought I had seen every awkward family moment, but this one sits heavy. My brother stopped praying, barely answers our messages, and last week he left my father's voice note on read. Now my mother looks at me over her çay saucer and says, quietly, "You will speak to him, won't you?" I am the one who still goes to the mosque, who remembers the verses by heart, and they believe I can bring him back. I want to help, but I am tired and afraid I will push him further away. How do you decide whether to step in for your parents or step back for the relationship?