A tenant having another person staying in the unit even on a permanent basis does not mean that person will become a tenant at some point. That person can remain there, as an occupant, as long as you’re not receiving rent from him/her, and the rent is still being paid by the tenant. The only way that person becomes a tenant is if all parties are in agreement to add him/her as a tenant on the lease, and that person then starts paying rent to the landlord.