I don't want my step kids around my baby

So, I'm currently 13w with my first child - my husband's third. He has two kids (ages 13 and 15) from his first marriage and I do love them. The problem is as they've grown they're childhood issues have escalated. They were always brats, fighting constantly and demanding... But then they'd be sweet and kind and funny... Recently though it's been scary. To the point where the fifteen year old, the boy, beat his sister unconscious. I truly think he is bipolar or something similar. His mother is, so it's possible he is too. The problem is he refuses help. He has already been attested more then once and is now in a sort of home for troubled boss. His sister knows his issues and instead of trying to help, or even avoid it, she antagonises him till he snaps. She then uses it to get attention.

They live in another state and when my baby arrives I want them to stay far away. I do not trust my step son (even though honestly I like him more than the sister). And my step daughter I also don't trust but for different reasons. I wouldn't even trust them to be in the same room with my baby with me and my husband in the room. I have not talked to my husband about this...

I feel like a horrible person, but I truly cannot think of them around my child without getting massive anxiety. Am I right in thinking this? How can I talk to my husband about it?