Riki77, been there done that with two siblings. Even though I was older than both of them and come from a FFB family, I knew I wasn’t strong enough to deal with them on my own. (Specially the one who went OTD when I was still living at home. My parents relied on me to help her the most since I was the “coolest” one living at home.) When I saw what I was up against, I got in touch with a great Rabbi in town (without telling my parents), and he was a lifesaver! Would not have been able to help her as much without it. She is who she is, and we still love her, but the Rabbi was great with her.
But there is always hope, the other sibling that went OTD, is the most Yeshivish in my family today. Just keep your head up and get someone to talk things over with.