Wife has turned against him because of her Twin Brother

My wife is a twin and her twin brother lives with us. Both of them are final yr students. Her twin brother’s attitude is unbearable. Imagine him bringing in his female friends into my house  in the name of "fellow student" in most occasions they passed the night in my house and throw wild parties especially if I travel and waste all the fuel in my cars and generators. I will only know from neighbors who will tell me when I get home. I have endured enough of this.

My wife seems not to reason with me rather supporting her brother. She say that I should let him be after all that he is no longer a child. She actually called me a hypocrite on one occasion stressing that that was how I was able to court her because when I met her, I was still staying with my brother at trans ekulu and we often sneak into the house. But as good as I can remember, I was very discreet and never threw my affairs up my brothers face and for crying out loud, that was my brothers house not my brother in law’s house and my brother was not financially responsible for me neither was he married. I pay this young man’s school fees, house him and feed him. I deserve some respect.

The one that pained me most is that once I bring up the issue, she will start giving me cold treatment. Only responding when I speak. Even the sex becomes horrible because she will just lie there on the bed looking into the open air. No emotions, no romance, no touching, I will just sweat it out and atimes I will lose my erection halfway and be frustrated out of her.

 I have talked to him man to man in a polite manner and I have threatened him, he stopped briefly yet he continued whenever I leave the house or travel.  Its when I come back, I will be seeing used condoms on the trash bin and cigarette stub littered everywhere. Sometimes in the middle of the night, I will be perceiving marijuana (Igbo) in my house but I am not yet sure if the smell is coming from outside or from his room. My fears are that his ways is a bad influence on my wife and detrimental to my image in the neighborhood. I have threatened to send him away but my wife said "if i do " she will give me hell in the house because according to her, he is part of her and that I accepted him the day I accepted her, that I am feeling too big and treating a full grown man like a house boy because I have money and he doesn’t have yet and so many silly stuffs that I cannot write here. Their parents are aged so I can’t possibly bother them with such a trivial issue.

Her reasoning baffles me . It obvious that she loves this boy more than me because she never sides me as long as it concerns him.

I don’t know what to do. I need opinions of wise people of this house  on how best to handle this situation with minimal collateral damage. I am no longer happy