I know they haven't met, but is your landlord at all aware you have those roommates?

If he (she?) is aware, ask for help. A lot of landlords have seen problem renters at some point or another and might have a decent understanding of the laws and regulations. If you've always paid rent on time an have no complaints, I'm sure landlord will be open to hearing your case. If they haven't bothered to meet your roomies, it's probably because you're responsible enough in managing the household that they don't feel the need to.

Document everything; maybe the guy can be cited for animal endangerment or something. It's probably better you two communicate over texts or writing because it's recorded rather than he-said-she-said. I hope the eviction process goes smoothly for you!