Guiding My Younger Brother Away from Premature Relationships

Assalamu alaikum, I’m reaching out about a delicate situation and would truly appreciate some sincere advice. I recently discovered that my 14-year-old brother has gotten involved with a Muslim girl from his school-they’re essentially in a haram relationship. I pieced it together when I stumbled across his social media activity. He’s a kind and respectful boy, but living in the West has exposed him to different influences, even though his friend circle is Muslim, which leaves me puzzled. I’m torn about what to do. Should I inform our parents? I worry they might handle it poorly and inadvertently push him away, causing him to hide things from me-then I’d lose insight into his life. Another thought is to speak with him directly, offer him Islamic guidance myself, and perhaps even have a gentle word with the girl. I’ve also considered telling our older brother-even though I may be more level-headed, he’s a male and might connect with him better. The core issue is that my brother is a teenager going through a rebellious stage, wanting to do as he pleases. I’m scared that if he’s dating now, he might drift toward vaping, smoking, or worse, especially since he’s not performing well or staying focused in school. Our parents may not fully grasp how youth behave or think these days-they’ve never had to navigate this kind of challenge. Please advise me on the best course of action, how to approach him gently, and what words to use.