sudden siblings

we recently took in my husband's 9 year old son for a few months. our daughter just turned 6, and is his half sister. he took her room, she sleeps with me and dad sleeps on the couch. not ideal. we only have a 2 bedroom.  they bug each other a lot. however, there are some concerns i have about the 9 year old. he was raised very differently from our daughter, and hasn't been a real part of our lives before now, due to extreme issues between his two parents, my husband and his ex-girlfriend (they were never married). our daughter comes to me occasionally about things he has said about private parts and such. one time, he was laughing to her and saying she had "nurples". today, he was saying to her that he had two balls. it just really bothers me that this is going on, as my daughter is fairly innocent in that area and previously never knew about that sort of thing. i am a little freaked out about it progressing and her being taken advantage by him when he hits more of the puberty stage. i just don't know what to do. i told him that i didn't want him talking to her about those things, but i feel like they should never be left alone.  any feedback?? it's so stressful to live in my own home suddenly!  

[Athena_M]

You are right about not leaving them alone.  What does your husband say about all this?  He should be the one telling his son what not to do.  You sound like such a good wife and mom.