Non Relative needing advice about small children

I have known this 23yrs old since she was 6yrs old. Her mother is my best friend. My friend now lives in SC and her daughter (which is really a relative foster child to her but daughter none the less)lives here. She (my friend) is not finacially stable. This girl has two small children a 1yr old and a 2 yr old. She has been pawning off these children since the day they were born. Her aunt has had them i have had them on several occasions as well as she has lived with me 3 times since this Feb and couple time before that. This last time she got mad at me and walked off with the kids with nowhere to go and two small bags of close and diaper. The is what she pulled alot with her Aunt, just getting mad and saying she is coming to get the kids. Then she is gone for a month or so then calls us to come back and get them becaue she has no where to stay. She wants nothing more to do with her family including her aunt but called me after 1 1/2 months of leaving my house mad saying she was being kicked out again and has no where to go can i take the kids again. I have a 3yrs old myself and can not keep doing this. Her children are suffering because she is selfish and stupid only thinking of herself and what she wants to do. My question is what can i do to keep these kids safe from her and stop her from taking them whenever she gets mad at someone or wants the money she gets from DCF? She has been living off welfare since they were born. She has never had a job. I don't know who to talk to about this. Everything I look at states relative temp cust but i am not family. And her family is done helping. These kids are suffering big time and emotionally and mentally. Her Two yrs old hardly even talks and is not potty trained or even been trying to potty train. He looks like he has lost weight this time too. I had to pick them up in a very bad part of town known for drugs at crime. They get so messed up after leaving and then coming back. What can I do?