Seeking Guidance for My Father's Struggles

Assalamu Alaikum everyone, I really need some advice about a sensitive family issue. It's been weighing on me a lot, and I’m hoping for some understanding and maybe a dua or two from you all. My dad is honestly a great father in so many ways-he’s loving, takes care of his parents, and has always been there for us. But recently, I’ve found out he’s gotten into some really harmful habits that are against our faith, and it’s honestly breaking my heart to see. He’s smoking way too much, and we all know that’s not good for him, but that’s not even the worst part. He’s also been drinking, and he’s been missing a lot of his prayers. On top of that, I accidentally saw something private that showed he’s involved in an inappropriate relationship with a close relative, which is definitely haram and has been really hard to process. I’m still just a teenager, and I’m at a total loss about what to do. I haven’t said anything to my mom yet because I’m scared it could really break up our family and cause so much pain. But I also don’t want to just stand by and watch my dad keep doing things that could hurt him in this life and the next. I really want to help him turn back to Allah and make things right, but I have no idea where to even start. If anyone has gone through something similar or has any advice on how to handle this with kindness and wisdom, I’d be so grateful. What should I say or do to encourage my dad without pushing him away? And honestly, I keep worrying about what might happen to him on Yawm al-Qiyamah if he doesn’t change... it’s a scary thought. Jazakum Allahu khairan for listening and for any support you can offer. May Allah make things easier for us all and guide him back to the straight path.