It depends on whether your written lease limits the occupants to those approved the landlord or not. If the lease gives the landlord some right of approval, or if it limits the number of people who live there, that provision is legal and enforceable: a lease is a contract, after all, and in signing the lease, you contractually agreed to limit the number or identity of people you could have live with you.If there is no limitation in the lease, you should be able to have your significant others move in: landlords may not impose limitations not found in the lease. It would be a good idea, though, to double check your town/city's zoning rules (contact the city clerk and/or building/housing dept.) to make sure that there is no very local rule limiting occupancy.