I've been with my FDH for 5 years and just recently got engaged. My relationship with his older two kids (sd25 and Ss23) is okay, it's not the greatest but they're civil at least. Sd25 just recently earned her Juris Doctor degree (law) and Ss23 is in his third year of medical school. My relatioship with the them is okay, it's not the best, but they're poliet and civil and we can have a normal conversations amongst ourelves. 

My main problems come from the youngest, Sd16. She knows how to play people to get what she wants, loves playing a innocent, and seems to thrive when she put people against eachother - basically me and FDH. BM actually sent her to come live with us because she was getting out of hand. She's your typical high school barbie type mean girl- all she cares about are her looks, popularity, boys, and social media. Fortunately FDH does not parent out of guilt. He calls her out on her crap, but it normal leads to shouting  match between the two of them, with her saying "I wish you would just die" or  call him "annoying". She has a lot of anger. 

6 years ago FDH moved states for work purposes, and this hit all of his kids hard, especially Sd16.  She was/is very much a daddy's girl. BM and FDH had to modifiy their CO with BM having the skids for majority of the year, but FDH would call, e-mail, text, and pay for their visit. He never stopped communicating with them, but I guess it still did bother to them in a way. When the older two siblings graduated from high school, they applied for colleges in our state, but they didn't live in our home. They choose to live on campus and find jobs that were close by. I would have no problem with them coming to live with us while in school- FDH even gave them both the option, but they had decided that they would much rather prefer to live on their own. Fortunately they were more direct with their feelings and said that they did have some resentment towards FDH, but they're were willing to work it out  with him. Things are good between the three of them. 

Whenever I try to talk to Sd16, disrespect is all I get from her. It's like the kid has marked me with a target (I probably do have one).  There was this one time that she lied about going to a friends house, but in reality she went to the beach with her friends. FDH would have let her go if she was just honest with him about where she was going, so when he found out (parent tracking on her phone. We pay for her phone), he went and got her and brought her home. Again another fight, and she was screaming at him and I probaly should not have gotten involved but it's hard to continue to watch her treat FDH with such malice. She told me to get out of her life and stay out and the best thing I could go for the everyone would be to kill myself. That's noting. The stories I could tell. 

She's not doing the greatest in school right now either, so I don't think she will launch in 2 years like her brother and sister. I've spoken to him about sending her back to BM but BM doesn't want her there either.  I can't continue living like this. I feel like I'm walking on egg shells in the house. When she's here, the atmosphere just becomes dark. Good note,FDH just put her in therapy, so hopefully that helps.