I 24 F have been with my current partner for around 3 years. About a year or so ago, we started to hang out more mixed family wise with both sets of siblings. During one of the first times my sister in law met my younger brother , she said in passing that he was cute. I hadn’t thought much of it and she pursued him then or attempted to and my brother declined. Told her he’d rather stay friends for the sake of family and also as she wasn’t his type. (His words not mine) He at one point even asked me to ask her to leave him alone as for some reason she would not accept his answer. My sister in law is very weird. She is someone who wants to be the prettiest on the room at all times , cannot stand to be near someone who looks better than her, constantly seeks male validation. In the past she has slept with her cousins bf while they were together . Also About 3 months ago she shared with me she had found the love of her life in a 19 yr old however he too cut it off with her. She is in constant competition with other woman to see who gets the most attention or always seems to be in the middle of drama related to men , the attention of men etc etc I know they way I wrote that seems off but I swear I don’t hate her. I had grown to like her in these years I’ve known her . She seems to be nice but now I feel like maybe she isn’t genuine I have tried hard to accept her as she is and to not judge her lifestyle choices Fast forward to now like a month ago, sister in law is again pursing my brother. This time he seems to be reciprocating the attention. When I ask him about it , he claims he still does not like her in that way and is talking to someone new .. she swears she friend zoned him although I know that’s not true by the way she gushes over him and is in constant contact with him I would not have an issue normally with this however some things bother me here 1) my brother still lives at home with my parents . She has been found in his room on his bed with him cuddled up. Did not say anything to my parents just snuck on in like a damn High schooler. Was discovered by my parent 2) she has a history of seeking male validation and I worry that is what she is doing but using my brother in the process 3) she enables my brothers smoking habit and allows my other underage siblings to smoke and drink at her place - super not cool btw!!! I’ve asked her multiple times to not get my younger underage siblings involved in her drug habits and she doesn’t listen I know technically my brothers a grown man but I just can’t shake this feeling I have My question- what do I do? Do I talk with my sibling about my concerns? Do I do nothing? How can I have a good conversation with him or her or both in a way that won’t damage my personal relationship with either? Do I have any right to feel this way?