Also when it comes to the bf smoking and drinking with your niece I’d be very weary of that and personally if possible I’d get one of my cousins that nobody knows is my cousin to handle him . Sorry if that isn’t helpful but personally that’s what I would do due to there being a very limited amount of legal ways to handle it .
Maybe try speaking to children services your self about this matter or maybe talk to the director of the foster care agency
Unfortunately the only thing you can do it just report it to cps . Have your 13 year old niece say something to the worker you report it to because they really need the kids to tell them in order to do anything and unfortunately even then they don’t take it seriously. The foster care system isnt a good place and they say they are here to help but they really just tear families apart . I’ve seen my aunt go through the same with her kids . You just have to advocate for them super hard and try to get them in your custody as soon as you can . I’m so sorry you’re sister , you , and your nieces and nephews are going through this . I really wish there was more information to help that I could give you .