I love my husband cannot stand his kids.

This is going to be a bit long, who ever reads through it without any Judgements, I thank you very much. 

My husband has 6 kids. One that is not biologically his but still considered his daughter. 2 of kids are not in his life as the mother took them away from him. So we're left with 4 now. We hardly ever see the oldest one (nonbiological daughter) because she got a job and going to school. She's a really nice girl so I never had a problem with her. Now we're down to 3 kids. The ones who give me a hard time!!! 

Let me start off with the 15 year old. Very sassy girl. Has an attitude about everything. My husband apologized in advanced when we started dating, letting me know how she was. I NEVER thought it was going to be bad.. how can a 15 year old make me feel like shit? Well I was wrong! She does. She's constantly disrespectful to me, talks about me, she's nice when she wants to be. I tried my best to be her friend and get along with her but it hasn't worked so far. From what I heard, she's always been like that with my husbands EX's. 

The 9 year old was at one point getting along with me. Was getting close to me but slowly started to distant herself ever since she started to hang out with her sister a lot more. She always would hang out with me, talk to me, want to help me out but now hardly ever talks to me. She's always telling her sister secrets which are obviously about me. I try to ignore it but it gets old after a while. I wanted to be able to get along with these girls and now it just went a whole 360 with this little one. She isn't rude but I can sense her vibe towards me. I recently heard from her brother that bother her and the 15 year old hate me for no reason. 

The 13 year old boy gets along with me perfectly we'll and does nothing to bother me, in fact he helps me out a lot. He respects me and never talks back even though I'm much younger than their father he never seems

To have a problem with me. 

I'm in an odd situation, I feel like I have no right to tell them what to do as they have their mothers and my husband to discipline them. I'm much younger than my husband and they know this. The 15 year old likes to bring up in a way to get to me. She likes to talk about my husbands ex's in front of me. Likes to bring up old shit that I do not want to hear. I spoke to my husband and it sort of stopped but I know it took it against me and hates me even more. She's extremely rude. And as much as I try to understand that I'm not their mother and they might be mad their parents arent together (it's been many years since they separated). I'm nothing but nice to these kids and they hate it even more when my husband has my back because he knows exactly how they are. I was okay with dealing with the 15 year olds attitude but now I feel like she's putting things into her sisters head (9 year old) 

Like I said, my husband has my back 100%. He'll do anything I say or talk to them about the way they behave with me. I didn't have a problem with the 9 year old until now. And I don't wether I should bring it up to my husband or keep it to myself since she hasn't disrespected me. It just makes me feel sad. I want to try and get along with them but they have just teamed up to go against me. I also want to add that I'm 8 months pregnant. This will be my first child..... I need advice ladies. Also my husband is 34 years old!