Roommate's girlfriend problems?

My roomate is almost like my brother, he very shy and has not had my girlfriends. He met this girl when he worked at office depot, she then moved about 5 hours away. I know she was fired, she sells/sold weed/drugs, and was arrest several years back for growing weed, I know her last relationship was with a woman and she has several pill bottles. I don't mind smoking, but made it clear no drug deals or creeps at my house. I didn't like her moving in because she's shady, wont say hello or anything, just staying in his room 24/7. He asked if she could stay for a week sometime, I didn't really say yes or no, and then brings her up, and never took her back home. I'm assuming she had all her stuff with her because its been months and they never went back. They now stay in their room literally all day, do not socialize, do not help sweep/mop and stuff, and are very shady. My girlfriend overheard her on phone saying" yea all i do is lay around and smoke weed and he brings me food" She has no intention on school, job, cleaning, or anything else. This is causing me lots of stress, and talking to my roommate has not worked. Its causing issues in my relationship, daily life, etc. and not sure what to do. Any suggestions?