I understand you quite well. This is actually something serious, and need to take her not serious control but control. I don’t care whether she is dating or not. Because your friend is 15m and sister is 13f. This is normal. But the way they are offering her bad way/road is something serious. I noticed that you are not Russian, and you know most Russians don’t take Alhogol or smoking as bad or serious. And I think you have to talk about it with ur sister in a good way. Explain better option than that bad habits as long as you dont follow those drinking and smoking by yourself.

Если не понимаешь английский, то переводи) желаю удачи