Thank you for your inquiry. I must admit that upon reading your question I couldn’t help but liken your situation to raising adult children. Those who know, know. It’s hard to have influence when you are unable to use tactics like, “Because I said so” or “If you don’t, I’ll have to take away your cell phone.”
Influencing others without authority can be difficult and feel impossible. And yet, influence isn’t only for leaders. Influence is the ability to change behavior in service of an important goal. For that, all you have to do is care. Caring is key to getting started. Hidden in your question are two possible assumptions.