The landlord can probably kick them out for having extra people living there that's not on the lease or for breaking something in the lease. (My parents are als

The landlord can probably kick them out for having extra people living there that's not on the lease or for breaking something in the lease. (My parents are also landlords, though not in NYC.) Of the places I've been in, the landlord knew about it and didn't care (not noisy or dirty), or it wasn't active enough to cause anybody to notice.