In my experience with 4 unrelated tenants in the same house, and there have been several. I have had to deal with a couple cases with extra people (permanent "couch crasher" and/or significant other) taking up residency. In both cases, I had a good standing relationship with at least one of the tenants. This allowed me to simply state my case, letting them know that I know they aren't living up to their end of the agreement, and that I have to report it to my client, the landlord, because he can be fined. With group renters like this there is usually one person that organizes the utility bills and so forth, that is usually the person with the ability to make things happen, the one you would like to carry this information back to the others. The problem, in both cases, was resolved within 10 days. I even helped the "couch crasher" find a very affordable room for rent. Offering them a way to fix it on their own should work. Offering them help can make them feel like you understand their situation. If in two weeks, if they haven't done anything to remedy the situation, there is always the same legal recourse you were already contemplating. Happy to help if I can.