My brother in law (36M) does not treat my sister (27F) with much kindness. No physical abuse, but he is lazy, immature, and is possibly emotionally/mentally abusive. I'm not a huge fan, parents aren't a huge fan, etc. He is always nice whenever we interact with him at family gatherings, but I've heard the stories of how he is at home when we're not around and I've never been impressed. Nothing to raise huge concern about (such as calling police), but I just don't like him, and I've given him chances to change his ways and he always disappoints me.
I (29F) recently got a new boyfriend (30M) who is wonderful. We met each others families, and before he met mine I warned him of BIL, that he comes off extremely nice, but I told him some stories about how he treats my sister and to not be fooled. I told him to be cordial, but that's it. And I'm only cordial because I've been told I pretty much have to be if I want to keep coming around. Well, my BF likes guns, so does BIL. And I do too. BIL has never made any effort to get to know ANY of the family, rarely comes to family events, etc. It's also another reason we don't like him a whole lot. He works in the same city I live (I do not live in the same city he lives in, or the rest of our family lives in). He has asked me for lunch recommendations in this city, but has never responded to requests to meet up for lunch when I have tried to extend an olive branch to get to know him. I don't even have his number, I have to message him through facebook.
This morning sister texts me saying BIL wants BF's number (BIL couldn't even text me asking himself LOL), and I already know it's because they talked guns and hunting when they met, which was fine in person, as I said he needed to be cordial, but that's where we want this to end. My BF is not interested in having a friendship with BIL unless he can start to have a relationship with the family he's been around for years, and treat my sister better.
TLDR: crappy BIL who has made no effort to get to know the family over the years and treats sister like crap wants my new BFs number. BF doesnt want to be his friend, how to politely say no.