Alice, My Fiancé's Awful Sister Refuses to Leave Our Apartment -- Ask Alice: Advice for Life at Home

Hi Alice, So my fiancé and I got our own apartment back in April of this year. His sister and her girlfriend have been "staying" here for nearly six months now, sleeping on my couch all day, getting up at about 3:00 pm and finally leaving until about 11:00 pm. They are rude to me, they had to pay rent ONE time but act like they own the place. So what's the best thing to do? My landlord knows they are here, and she wants them out, I've had two infractions for them being here but I can't get them...