tenant has live-in nanny, against lease

[Zigner]

However, such a lease provision may well violate the federal Fair Housing Act (FHA) and/or applicable state laws that prohibit discrimination based on family status. Occupancy standards must be reasonable and not discriminate against families with children. The FHA has set a rebuttable presumption that a limit of two persons per bedroom is reasonable. See the FHA Keating memo, which has been incorporated into the Federal Register as official FHA policy. Even a limit of two persons per bedroom may not be reasonable in some circumstances. For example, a federal court held that such a policy was unreasonable when the renters were a married couple with an infant renting a one bedroom apartment. If an occupancy limit in a lease violates federal or state fair housing laws that restriction is unenforceable.

It may, or it may not. If the limitation is based on "occupants", it would be less likely to run afoul of the FHA than if the limitation is based on "children". It is fact-specific. (I am not trying to contradict you, rather, I'm agreeing with you and just expanding upon it.)
My earlier statement should not have sounded as conclusive as it did, and would be better stated as "If the tenant signed a lease for one occupant and then moved in additional occupants (not just a daytime nanny) then that may be a breach of the lease".

 

[Zigner]

Not when children are involved. A landlord cannot prevent a tenant from having children - only the number of children should the number exceed the allowable number for the size of the rental (e.g., 2 people per bedroom).

Even such a limit may not be enforceable. See TM's reply (and my response to his reply).

 

[quincy]

Even such a limit may not be enforceable. See TM's reply (and my response to his reply).

TM essentially was saying what I said (but he used more words ).

There can also be city codes to consider. For example, although federal occupancy standards set as reasonable 2 people per bedroom, Nashville’s property code section 16.24.400 permits no more than 3 unrelated adults per unit, regardless of the number of bedrooms. https://www.nashville.gov/Codes-Administration/Property-Standards/Code-Enforcement/Property-Maintenance-Code.aspx

It can get really tricky when tenants have additional children during the course of their tenancy. A landlord cannot evict a tenant for having more children, although a lease once expired does not have to be renewed.

 

[Zigner]

TM essentially was saying what I said (but he used more words ).

Essentially. But your post actually made the same mistake as mine (being too conclusive), just in the opposite direction.

 

[quincy]

Essentially. But your post actually made the same mistake as mine (being too conclusive), just in the opposite direction.

Ah. I should have added a “potentially.”

 

[FarmerJ]

If you are going to try to treat this problem as your tenant has a unauthorized person living with them then its going to be up to you to prove they are violating the lease. Other wise what you didnt say was how much time there is left on the current lease? I get it that the neighboring unit had it pretty good with a quieter neighbor but I cant help but wonder how old the structure is and do you know for sure if there is anything to sound proof between them ? If not then perhaps you may want to explore either doing it your self or hiring it out and having insulation blown in between the units ( yes there is going to be some wall repairs ) but if you sound proofed between the units the one who is not happy about the noise may find it much nicer and be willing to stay put ( even if you dont renew with the other tenant.