What do I do about this "man" grooming this little girl?

Question

So, first of all please no judging me. Be nice or leave, thanks 
I live in an Oxford house 
For those of you that don't know it's where people with drug/alcohol problems live with other addicts to maintain sobriety. So everyone in the house is sober. There are about 15 people in the house, including 5 minors. Now, I wouldn't want my children to be in a house filled with criminals and addicts without knowing their background (no one here getsa background check!) so that's the first issue I have. 
Enough ranting I'll get on with the story...
There is a 26 year old male who lives here. He is "disabled" and doesn't work. He claims to be schizophrenic and has diabetes. He is very immature and acts like a 12 year old. A lot of his stories don't add up and he lies a lot. 
There is a 13 year old girl who lives here. When we first moved in this other guy, let's called him A, didn't live here. The little girl, we will call B, was very nice, polite, hung out with her brother, was nice to another little girl who lived here, and was just pleasant to be around. A normal 13 year old girl. Well ever since A got here, she's been different and I've seen ALL signs of grooming. And having been groomed as a child I think I know.
Seeing this post grow longer so i will just name the few key things that have happened to make me uncomfortable... He hangs out with her EVERY. DAY. ALL. DAY. No joke. He has pictures of B on his phone and he has her number. They have both disappeared for about 20 mins with no one knowing where they are and then they both randomly show up. She has been in his room alone when it is a house rule that NO ONE is allowed in our rooms. She has had major attitude shifts. She is extremely rude to her brother (I let this slide. He's 10 and she's 13, being kids can be hard.) She was friends with another little girl in the house but started being so rude and mean that the parents of that little girl moved her out (parents told us this). B also yelled at her dad. A isolates her from everyone in the house. Recently two teenage boys moved in around her age and whenever they come around he tries to distract the boys away from her... It's weird! We recently had a snowstorm and they had a snowball fight. B hit him in the balls with a snowball and he later was talking to her about his balls... They also sit on the same couch. He has painted her toe nails, bought her gifts. A lot of other shit has happened but this is what I can name for now. Im sure you're thinking, "Have you said anything to the parents?"EVERYONE IN THE HOUSE HAS. The house manager has talked to A about 3 different times about the relationship A has with his daughter and each time A has been super defensive. Just weird as fuck. We have talked to the parents. The dad tells us "He has the brain of a 13 year old he isnt as developed as us." Even if this is true, I dont think he should be around children. What should I do, if anything?
All questions will be answered as an edit on here... If I like your question, come check for edits...
*EDIT* He doesn't see himself as a child. He very well isn't mentally disabled in that way. He knows what he is doing is wrong. Plain and simple. He even says he has a child of his own.
Also, I'm not sure how to gather evidence without having a phone strapped to me recording 24/7. I try to stay far away from him and I barely even leave my room.
*EDIT 2 this is legal and 100% real.  I wish I could give more info but I want to remain anonymous. Our house isn't separated by sex. I know that there are places that separate by sex but ours doesn't. Anyway my partner and I will be making a report soon. We have said something to the upper management and sadly they don't seem to care as much.
Another Edit* I think I need to reiterate that this guy is NOT developmentally disabled. 
The parents of this girl stay in their room in the basement while the kids have free run of the house and she mainly stays in the living room with A. And he knows he is wrong because everytime someone comes into the room they scurry like they're doing something wrong. HE IS AWARE HE IS NOT DOING SOMETHING RIGHT

Answer

Wait how is this living arrangement legal??

Answer

I have an Uncle who is developmentally delayed, he too acts around 13. He will tell you and everyone that he is an adult and can make his own adult decisions but we all know this isn't true. To the normal eye he looks and can even act like your average 60 yr old male. It's when you sit down with him and get to know him over the years is where you see the childlike behavior.  Growing up I would spend hours in his room listening to the Spice Girls and he made it very clear that I was his best friend and would get very possessive of me at family gatherings.Personally I think its wrong of you to put disabled into quotation marks as if this is somthing he is making up. His behavior seems weird to you because it's not normal but it doesn't mean he's necessarily harmful or grooming this young girl. Her attitude change can very well come from her age  (impending period) or the fact that she is living in a group home. If their are house rules that they are breaking then yes those should be addressed but I wouldn't go pushing for people to start labeling him....

Answer

If he's genuinely got the mentality of a child, then he doesn't see anything wrong with what he's doing because in his eyes, he is a child. If the authorities agree he is mentally disabled and of a much younger mental age, then there's nothing untoward. The way you described their relationship, if you hadn't said it was a young girl and a man in his 20s it sounds like a normal childhood friendship.
I think you are letting your own past interfere here. I remember a man older than me with the mental capacity of a child being SO proud of his teletubbies videos he had with him... Anyone on the outside also would have thought that was weird.
Also this isn't a controversy, anon.

Answer

I don’t think this is legal. Oxford Houses are typically separated by sex. There was both male and female homes not too far from my house when I was growing up and the women with children were in an entirely different building. I feel like this whole ass building needs investigating.

Answer

If this man acts like a 12 year old, and has been diagnosed with having the cognitive function of someone much younger, then he obviously doesn’t have the understanding.
It is the home’s responsibility to protect both him and the girl, though the protections they both need differ quite a bit.  
I’d be calling the owners & management if the parents aren’t doing anything.

Answer

I would be calling the cops although idk if they could do anything at this point. I do think that if everyone had made complaints about him then he should be told to leave the house. If I'm not mistaken those houses don't have leases & are more follow the rules & you can stay, right? Maybe you can try to talk to the girl, too.

Answer

Gather evidence and take it further???????

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Call child services. If the parents won't protect her, you need to.

Answer

I’d report it and let cps investigate it.

Answer

I assume the family is getting some type of government pay to house the sober living residents? In that case, there must be a regulatory agency that oversees it. I would reach out to them and let them know or call child protective services.

What do I do about this "man" grooming this little girl?

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