So my boyfriend had i have been dating for over 3 years his brother (we'll call him D) and i do not like each other but are always civil if we have to be at the same family event or something. I'd heard he's a bit of a womanizer but i didn't feel it was any of my business. My boyfriend's buddies would tease D whenever he would come by saying stuff like "hide your daughter" about a year ago D convinced one of his friends to move here with his 16 year old daughter. D was 26 at the time. And i believe had just got out of the military. D was the only person this girl and her father would know out here. She'd be starting at a new highschool at the end of the summer. So she had nobody here except her father whicshe has a horrible relationship with and from what i gather not many people liked her back where she was from. Within a month people were making comments saying stuff like "oh D and that girl sure do have an interesting relationship." She may aswell have moved states and she had no friends back where she was from so she pretty much worships the ground D walks on which again isn't really any of my business but i always felt off around D. It's hard to put into words but he's one of those people where the smile doesn't reach his eyes. Anyway i let my boyfriend know i didn't like being around his brother and probably wouldn't be going over to his mom's for a while. (D moved back in with his mom after he moved back here) That's when i find out that when D was 20 he was accused of statutory rape of a 15 year old girl. Nothing ever came of the charges and i'm not sure why. So fast forward a couple weeks and D's mom decides to have a conversation with D, the 16 year old girl, and her father. And from what i understand D's mom was concerned about this girl having a crush on her son and wanted them to take some time apart and let her find friends her own age. Not hanging out with 26 year old men everyday. D apparently looked like he wanted to kill everybody and didn't open his mouth. Fast forward to now. The girl is 17 D is 27 he's taking her camping alone. He takes her up in the mountain alone all the time to go riding. She got her dad to buy her the exact same car as D. D got the girl and her father into the same sport he likes. More people than ever are questioning if they're dating. I feel like puking everytime i have to be around D. And her father said that he prefer her to be with D instead of "some stupid teenager." now that school is back in she joined sports teams and D is going to every game. The other day she got into a fight with her dad at a party they were having and D was there she ran out of the house all dramatic and D had to go look for her in the woods.. They were gone for hours according to my boyfriend.
And literally nobody has the nerve to sit them down again and say "hey some boundaries need to be set here."
Idk to me there is something very wrong when a 27 year old man wants to spend all his time with a 17 year old girl.
And being a survivor of sexual abuse myself it makes this even harder to see. And i hate myself for being too scared to stand up for her especially because she doesn't see how it's wrong.

Tldr; 26 year old man covninced single father to move with his 16 year old daughter. Once they got here he isolated her from people her own age and now she spends all her time with him.
Taking her places buying her things. Her father would rather her be with him than a teenager.