Notice required for a landlord to give to tenants when selling off-market (WHOLESALE)

[Sham Haile]

Hey, BiggerPockets community I am curious about landlord-tenant laws in Seattle when it comes to giving a tenant notice to sell a home as a landlord. 

The tenants have been aware of the landlord's intent to sell for at least 3 months now. When asked how much time they need to move they brought up the 90-day notice law in Seattle and the requirement that it must be written. This in turn could turn away buyers/delay possession to a buyer who wants the home delivered vacant. 

For a month-to-month lease that isn't under any lease agreement, what could the seller legally do to get the home sold off-market?