If a tenant wants to terminate the lease early, what can the landlord ask for?

The building is owner-occupied, and a one-family dwelling with 4 rooms, three of which are being rented out, however, there is no rental permit (which should be okay because it is owner occupied). The lease is for one year and they want to leave two months early. Additionally, they have violated the lease by installing and modifying their rooms, though we didn't say anything at the time because we didn't know.