What should I do with inherited tenants that had verbal leases with prior owner?

[Matt Bowers]

(We're in Seattle.)

This is my first post on BP!

I'm closing on a triplex on July 31st that currently has tenants. The tenants are all month-to-month but two units only have verbal leases. Repeat: NO written lease. We want to raise the rent by about 15% for each. I was going to raise the rent 9% after 30 days and up to 15% after 60 days. The part I'm confused about is if I need to sign a lease on day one, or if the current verbal agreement is sufficient. We did sign estoppel agreements with all three tenants. We do not have previous applications from the tenants.

How would you handle this? Thanks a lot!