Maybe your stepson just has a bad psychologist.
As Mom, I would go with my gut. The fact is your SS was sexual with her, even if he didn't moleste or rape her. And nobody knows what he did, really. Kids normally do not tell all at first. You find out much later, after the predator is not in their life.
As the mom of two daughters, my own mom gut tells me that the fact that SS was sexual at all means that nobody, including a great psychiatrist, can guarantee your daughter will be safe. She doesn't want to live with him. She should never have to again. I would say she should never have to see him again. What if this boy was not your stepson? Would you let your daughter be around him? Force her to interact with him?
I don't believe talking to relatives helps, although they are now on the side of residential. I can't see how asking them is relevant. They arent professionals and are biased. You are her mother. This is serious. Even your son can not have a final say. if we are using fairness as the meter, SS should leave. But this is about safety, not fairness. Even if SS gets help there is no guarantee he will be safe. Ever. Sexual problems are one of those things that sometimes can not be treated and why should your daughter be the guinea pig?
I still think your husband's attitude is "off," in this. Often men don't understand sexual abuse unless it happened to them. And he is in denial about his son. And it is perpetrated by this psychologist. Not all psychologists are good. This one is frankly behaving oddly about this. Very.
Yes, get daughter a fresh female psychologist who deals with sexual abuse because even taping her in the shower is sexual abuse. You know that he did that. Make sure the new psychologist is in no way attached to the SS family. I still say different city. And you, as Mom, need to protect your daughter. Nobody else in this mess is worried about her. Just you. Do YOU have relatives?
Do not be surprised if you find out later that SS did more to her than she is admitting for now. A patient, caring psychologist ,(not just a counselor/therapist) schooled in sexual abuse will slowly gain her trust so that she can feel safe enough to tell all. That is the type of professional who helped my kids when both were saying it was "just a few times." It took a year to learn it had been three years.
Also sometimes abused kids forget the abuse and it comes back in flashbacks as they become married women with husband's and kids. Often it is hidden in the sub conscience until it causes big problems later. My daughter and son know R. abused them but neither remember what he did. The mind blocks out horrible memories but then they can come back. You don't want that for your amazing daughter who did nothing to deserve this. At the very worst it can turn into multiple personality disorder. Not usually, but that shows how the mind can repress trauma. That is the mind blocking what happened because it is a huge trauma.
Sadly I think daughter will heal best away from SS forever.I don't know how one can heal with the abuser around being treated like a good guy. And he seems to be getting more sympathy than your daughter. It's backwards.
You are overwhelmed by all these relatives and psychologists of SS. But you are a Mom and you know best. Don't let this family obscure the real problem and do what's best for your daughter. I assume your son will be in college next year so his desires can not trump your daughters needs. It's too critical. Your son will be better off without SS too. Trust your mom gut. It's on the right track. This family of SS smells. They just want to protect SS. Wait until he does something to a girl outside the family. One not afraid of his family.
Love and light.