I am not licensed to practice law in the State of Washington, and with that understanding I will attempt to answer your question. There is usually language in a written Lease Agreement which indicates that prior to termination of the lease period, one party or the other must give a certain amount of notice to the other party of its indication to re-new or terminate. Leases usually also contain language indicating what happens in the event there is no such notice given. Sometimes, the lease automatically re-news, but usually the lease is converted to a "month-to-month lease" until the Landlord or the Tenant give 30 days notice of intent to terminate (or until a new Lease Agreement is signed). I suggest that you go back to the Lease Agreement and read it carefully. Your answer is probably contained in the document.
Most likely your tenants are on a month to month lease agreement at this point. It sounds as though the initial 1 year lease has expired, and the 6 month lease expired 2 months ago. If you have accepted rent beyond those terms, a month to month agreement would most likely be determined to have been made by the actions of paying rent and collecting rent. It sounds as though the tenants have lived up to their requirements under the written leases as far as length are concerned so you probably could not say they broke the lease. You still probably have to honor last months rent, and you must give the deposit back also minus any damage they caused beyond normal wear and tear.
A hold over clause basically outlines what happens at the end of the lease term. It usually incorporates the terms of the lease in case the lease term expires without a new lease. Without looking at your lease I cannot tell you what it says, but most clauses state that they term will go month to month after the initial term of the lease.
In order to terminate a month to month agreement, either side may provide a 20 day notice to terminate the rental for nearly any reason (you may not issue one for the reason of discrimination under the protected classes). If there are less than 20 days left in the rental period, the notice will be deemed to apply to the next rental period. (Probably the end of August).