Sorry to have to tell you this but you are probably going to have to evict them through the courts because they are tenants.
The Washington landlord tenant statute Section RCW 59.18.030 Definitions:
(24) A "tenant" is any person who is entitled to occupy a dwelling unit primarily for living or dwelling purposes under a rental agreement.
(22) "Rental agreement" means all agreements which establish or modify the terms, conditions, rules, regulations, or any other provisions concerning the use and occupancy of a dwelling unit.
Note that there is nothing in the definition of "Rental agreement" that requires the payment of rent for an occupant to be a "tenant."
Section RCW 59.18.290 gives you the requirements for removing a holdover tenant after the termination date:
Removal or exclusion of tenant from premises—Holding over or excluding landlord from premises after termination date.
(1) It shall be unlawful for the landlord to remove or exclude from the premises the tenant thereof except under a court order so authorizing. Any tenant so removed or excluded in violation of this section may recover possession of the property or terminate the rental agreement and, in either case, may recover the actual damages sustained. The prevailing party may recover the costs of suit or arbitration and reasonable attorney's fees.
(2) It shall be unlawful for the tenant to hold over in the premises or exclude the landlord therefrom after the termination of the rental agreement except under a valid court order so authorizing. Any landlord so deprived of possession of premises in violation of this section may recover possession of the property and damages sustained by him or her, and the prevailing party may recover his or her costs of suit or arbitration and reasonable attorney's fees.
The entire landlord tenant statute is at:
Chapter 59.18 RCW: RESIDENTIAL LANDLORD-TENANT ACT
If they are still there after tomorrow you will have to evict through the courts.