ok I really need some advice

So my 2 SIL (one is my bfs sister and the other is his brothers gf) and their combined 4 children moved in with use because of the hurricane. 2 of them are so bad it is sick, but that isn't the part that has really got me. So almost as soon as they move in the sister meets this guys through her brother (also my bfs brother) and my bf doesn't like hime because he used to beat the crap out of his ex gf. the sister knows about this but believes him when he says "it wasnt me," how many times have we heard that? At first my bf would always argue about it and i flipped because it was messing with our relationship. so he just said he didnt want dude near the house. so dude was alone for thanksgiving and the sister really wanted him to come over, so i begged my bf to let him come over. he agreed but stayed in our room all day. this was supposed to be a 1 time thing. well this man has been coming closer and closer to the house. this afternoon he was next to our car talking to her and just about 30mins ago she had our shed opened and he was next to her. wtf business do you ahve in our she anyway? I feel like she is disrespecting our home and i am so mad about it. am i just over reacting?

to clarify: i dont care who she sees, i just don't want people like that around my home where we rest our heads, where my child sleeps and despite setting boundaries, she still doesn't care. This is not an apartment complex, it is my home in which i own. So i feel it is blatant disrespect.