My Sister's Mental Illness is Ruining my Life

TLDR: My sister is a mental illness mess and wants to drag her children down with her. I am afraid for the kids. I am doing all I can think of while working and taking care of a 12mos old.

I just want to know what are you supposed to do with this situation? Does anyone have any tips that have gone through something like this? I feel like my family is on a separate island trying to contain this and make sure it doesn't get out of hand but that feels like it's just too late.

My sister is 34, she has 3 kids, R(14), A(9), M(12mos), she has been diagnosed with bipolar depression since M was born. I am not sure what exactly triggered her melting point but it wasn't when she moved back home, or when she immediately gave birth, but she was never a good person. When she was a child, she stole money from my parents, and crashed a bunch of cars. I never really knew her when I was growing up because she was always out of the house with her boyfriends, I just watched and absorbed my siblings' mistakes. My sister got pregnant at 20years old and she tried to REDACTED, I don't know the details but that was when she went to the mental hospital the first time. She had her second kid and that seemed fine with her mental state, she moved out of the house and I saw the kids frequently. 
Last year she moved back in and broke up with the baby daddy, it was a big adjustment for us all, no shame it's tough out here in the world. I feel like ever since she saw Chad, the Youtube guy on “The Necessary Conversation” her brain flipped and she went head over heels with him and somehow started dating him in her mind… We didn't realize how bad it had gotten but we noticed a degradation in her personality and her work. Eventually, she flipped out and told her boss that the truck she drives smelled like fire and that it was going to blow (she filled it with the wrong gas and basically ruined the van). At the same time she was driving up to see the baby daddy, for some reason, the car she had had weapons in it from my dad, so we thought she was going to kill him. My sister got lost right before the tunnel to his place and stopped, cops say in the middle of the road and she gave them Chad’s last name, she says she pulled over to look for her phone. But she left M in the car by himself, and she went to the hospital and my mom and I went to go get M. I took the car home and my mom went to the hospital with M. 
A while goes by and my sister comes back, she seems fine, maybe “back to normal”, she is going to therapy and making sure her kids go to school, but like always she doesn't want help, not even with the baby. She starts talking to things like in an offline video game she said the “NPCS were having conversations with her”, it's a co-op game but with those bots. Then, she starts talking to Chad in her mind thinking that he is coming to get her and the kids, no one ever shows up. One night I hear screaming and I come downstairs to the kids on the couch huddled together, A is crying, R is in a mix of emotions, anger, shock, upset, M has no clue what's going on but is calm. My sister is yelling at my dad accusing him of things that I know he didn't do, but I can see how she got it mixed up from all the stories he has told. My dad is similar to my sister but lacks the responsibilities to care about anyone else but himself, he just has visions and that's the end of it, whatever my sister has its genetics mixed with whatever drugs she is taking, weed, alcohol, and prescribed meds that amplify if mixed with those.
Eventually my mom calms my sister down but the next day she goes back to the mental hospital. She stayed for about a week but the hospital regretted it when she signed the papers to leave because she was not ready. Since then she has been talking to Chad daily in her mind and willing him to show up. She is even going to the hotel up the street “because that's where he is”. Just a few days ago she went to our state's capital and got lost, but got pissy when my mom offered to help her because she “is a grown woman”. When she is “watching” M she is just on her phone usually crying, we take him away because M likes to get into stuff and she acts like we are the villains for taking him.

I am afraid she is going to try and take her kids away, she has no job and her kids do not trust her. She lacks accountability, responsibility. I don't think she would hurt them but my gut says she isn’t trustworthy with everything she has done. We have my sister on a tracker and we are getting cameras. I will be recording her when she is doing weird shit or ignoring her child. I probably didn't need to add all of this and I know I am missing a bunch of stuff, I am a bit all over the place with this post too. I am just typing this out as I start to head to bed. I would like advice, if possible or to not feel like I am alone, I talk to my friends and family about her but it still feels like we are alone in this. I am worried for my sister but I am mostly worried about the kids. It's not fair, it's not fair that R thinks he can somehow fix his mother, it's not fair that all A wants is for her “mommy to come back”.