A lease that is not notarized will not be enforced past one year. The only loophole is if you have made substantial improvements to the property to indicate that you intended this to be longer than one year, this situation in very rare in standard landlord tenant relationships.
Regarding the new owner, they may not have to honor the lease because it is longer than one year. But, Seattle does have a Just Cause Ordinance which requires a landlord to have just cause in order to evict you or terminate the tenancy. Examples of just cause would be failure to pay rent 4 times in a year, violating the lease agreement 3 times in a year, or more specific to your situation, the owner sells the house to a new owner and that new person would like to move into the property to make it a primary home for himself his immediate family.
This is something that you should discuss with your attorney before making any decisions.
This answer is for informational purposes only and should not be construed to establish an attorney client relationship. Before taking any legal action, it is always advisable to discuss your specific situation with an attorney.