Apologies if this isn't allowed or is not the best place.
Need advice on how to prepare myself and on what all my upper management (UM) is and is not allowed to do.
What caused the situation was someone at my work used to date another worker there. She was underage, he very much was not. We'll call her Kay and him creep. After they broke up, he would not stop trying to talk to her and she went to UM to complain about the harassment. UM knew of their relationship and didn't put an end to it, and also have allowed him to keep working at the establishment even alongside Kay, despite the wrong relationship and harassment. Kay didn't know what to do and ended up just dealing with it for a couple years. That is the background.
The current situation: I started working there and became friends with Kay. They ended up telling me about this and I was very upset about it. I brought it up with UM as I was uncomfortable and rather pissed. Since then UM has spoken with both of us, mainly just trying to claim he wasn't aware and it wasn't his fault. For now neither of us will be scheduled with creep anymore, and they are going to have HR do an investigation. However, there's a lot of scummy stuff.
One, during Kay and creep's relationship, creep was spoken with and warned by police but continued to date her.
UM did not put an end to anything or do anything to make sure Kay was alright or comfortable. Kay was told to handle it how she wanted to and that there wasn't anything UM could do.
UM (single person) and creep are friends. Creep has been there the longest and even lived with UM for awhile.
Kay and I were both told to keep the situation confidential or there could be problems with our jobs.
All other managers were told that if they were to discuss the situation with either of us they would get punished.
UM told Kay that we might not be able to work together anymore and has been putting heavy emphasis on it affecting her job.
UM told Kay that they would speak for her with HR and that she didn't have to be a part of the conversation for the investigation. Also said they probably wouldn't be interested in speaking with her anyway. We are having NONE of that. She has made it very clear with him multiple times that she wants to be there for the conversation and I told her I wanted to be as well.
Lastly (for now) UM told one of the other managers that they only brought hr into this to save his ass.
Any help on how to approach this situation and what to do, and the legality on all of this would be extremely appreciated. Sorry for the long post; thanks for your time.