Blended families

I have a daughter my husband has a son.

My daughters bio dad doesn't see her & my daughter sees my husband as a father figure. My step son is with his mother on weekdays. She has told him not to call me mom, said that my daughter is not his real sister, said that he doesn't need to listen to anyone except his dad. When he comes over it is like we are all divided, & he is always saying he has to do what mom says. He even came to our house last weekend talking about divorce asking if me & his dad would get one(we do not ever talk about divorce) then gave an adult explanation on what divorce is to My daughter who asked him what it was.

My problem is my daughter is with us 24/7 step son weekend's so my husband has guilt issues. My husbands mother & my step sons mother accuse my husband of not caring about his son because he is 'always with his wife's daughter'. So when my step son comes over he gets away with most things, he is mean to my daughter he complains about everything..he even yells at my husband saying things like 'that's why I hate coming over here!' if my husband corrects his behavior at all or makes him eat a meal he doesn't want or go to bed on time anything at all. My thing is my husband is not choosing my daughter over his son! He sees her everyday because I have her everyday! If he had a choice he wouldn't pick to see my child everyday & not his. My step sons mother requested him to only have his son on weekend's..at their last court hearing he requested more days & she said absolutely not & the judge went with that. Basically it feels like everything my step son does is acceptable which I don't think bullying your step sister is acceptable behavior. I don't think screaming at adults is okay. My husband & my step sons mother were never together, before she got pregnant they were in a relationship for 1-2 months. I don't know what to do. Everyone always wants to view the step mother as evil. All I want is my daughter to be treated with respect & to not be bullied by her brother & for my husband to handle his behavior when it needs to be corrected. I feel absolutely stuck especially when half the time that I try to talk to my husband about this & he refuses to. ;(