Suicidal Foster Child in my home. Is she dangerous?

I have 3 girl Fc. 10 yr. Old, 12 yr. Old and a 6yr old. The six-year-old is is my Bio Grand FC. The 10-year-old goes on visits Every weekend , the 6 year old also has visits and the 12 year old does not Have a visit and rarely has contact with her mom. The 12-year-old shares a room with my six-year-old bio grandchild. My grandchild recently caught the 12-year-old putting urine in her doll house tub. When I questioned the 12-year-old about the urine she put in my six year old grandchild’s dollhouse she had no answer. The 12 year old lies when confronted. The 12-year-old has made mean remarks about my six-year-old grandchild and seems irritated with the 6 year old. The 10 year old seems jealous of my grandchild and has choked my grandchild in the past and purposely smashed her finger. I had a talk with the 10 year old. The 12 year-old is reclusive , wets the bed and stays in the room with the door shut all the day. I just moved the 12-year-old and a 10-year-old to the same room. I saw a lot of sharp objects and lighters in the 12 year old room during the move. When the 12 year old return from school I asked to see her wrist. They were cut up not deep but cut up. I had no idea. We do not have a relationship And she does not talk to me at all. My butcher knife went missing and mysteriously reappeared. The 12-year-old wonders the house at 2/3am in the morning. I sleep hard so I don’t hear her but others do. The 12 year old is reclusive doesn’t say much but I’ve Found letters That she wrote seeming very angry at her mother. My bio daughter does not trust the 12 year old or 10 yo In the house or around her 6 year old child. Am I putting others at danger with these foster children 12 yo in my house? Is this 10 year old a bad fit? Are all these children Ill? I contacted the social worker and she did not answer I have a feeling she knew about this and did not disclose this. The 10 year old is going home soon. I really want to help the 12-year-old but I don’t know if this is the place for her. I’m starting to reconsider this whole foster thing. What should I do? P.S This is only my fifth foster child.