my brother rents a room in our house...

Sarah • 27. Married. My son was born 2/22/16 and his little sister 7/5/17
My husband and I agreed that we would let my 28 year old brother rent from us for $200/month to help get him out from under my parents roof- it was a long time coming and we get along with our parents great but he just didn't feel right living with them any longer... so a few months before we moved in my husband and I were expecting our first baby and the plan was that my brother would be out before baby came, we'll our son is 2 now and he STILL lives with us, and we're expecting number 2 this July! We gently tried to give him a push out the door but felt bad that he had no money saved up and would have to go back to my parents soooo, we agreed to ONE MORE YEAR-- yes it's gonna drive me nuts but it's $200 a month we get extra ANd he doesn't have to go back to my parents.:. I feel $200 is a very very generous amount to expect from him considering most people would rent a room for double that. Now my only highly unreasonable issue with him is that for the past 6 months his girlfriend stays over on the weekend... EVERY FREAKING WEEkEND... and usually once during the week- they don't eat our food, and they typically stay in his bedroom all weekend long, which is odd to me, they are both recovering drug addicts so that makes me uncomfortable- when I ask questions about what they do all day they get very offensive, I suppose it isn't my business but I do have a child in the house- she only showers here once a week when she stays for weekends. Idk how to tell him she can not stay all weekend every weekend... he would probably argue that he pays rent and should be able to have who he pleases , while yes it's true that she doesn't shower here much and mostly stays in his room I still feel kinda screwed over by the situation. Idk why I'm so pissed about it, I don't really trust either of them and I'm trying to build a family here... I'm so torn on weather it's right and fair for me to ask him to cut her overnights here- again he does pay $200 a month but she doesn't pay anything, she also doesn't use much here though. Ugh I really just want my house to myself and my family and felt kind enough giving him another year but the girlfriend can't be here 4 days a week!
Edit: what makes me suspicious is that temhey lied about how they met, they said mutual friends but one day when his gf was drunk she spewed that they met in an outpatient program... my brother still doesn't know that I know the truth and I get that it shouldn't be my business but with him living with me I feel it IS my business. She has been sober a lot less longer than he, not that it matters but she took something one day she claimed she got from a friend for her anxiety and swore it was a one time thing/.. I've grown up with two drug addict brothers and know that's total bs. She didn't agree it was a relapse simply because it "was never her drug of choice" I don't want more money honestly I just need to figure out a way to say hey I'm sorry but she can't stay here every weekend... my brother is VERY sensitive and easily offended, I don't want to ruin our relationship but I do feel he is abusing our kindness. Also she doesn't work, she had a job working with disabled kids but then got arrested for substance in her car and they let her go, otherwise in sure they'd have a place. She also lied about the job and acted like she still had it I only know the truth bc I happen to know someone who works at the same place, you bet I called her out// I'm sure it would be embarrassing to say but this entire thing feels like lies I too of lies.