Tenant Occupied with no lease

[Andrew Gudmunson]

Hi all! I've been really bad about staying updated with the BP forums! :/

A little background on me, my wife and I live in rural eastern WA and are currently house hacking a duplex. We're looking into purchasing a second duplex via owner financing and have been in negotiations with the current owner. According to the current owner he's had no issues with the current tenants, there have been no late payments or anything of the sort, but he's never required a lease to be signed. He currently has both units quite a bit under market value. The property is two stories with a finished basement. The bottom unit has 2 bedrooms and 1 bathroom on the main floor and one bedroom with another bathroom in the basement. The upper unit is a 2 bedroom 1 bathroom on the top story. Each unit is about $100-$150 under current market value. 

I'm quite inexperienced with this kind of thing and was wondering if anyone could lend some advice on how to deal with this type of situation in WA state. Will I be able to require the tenants to sign a lease once the purchase is complete and will I be able to raise the current rent to market value? I'm familiar with cash for keys but I would like to try and make things work with the current tenants before putting more money into the deal, especially if they've been as good as the current owner states. 

Anyways, any advice would be much appreciated! Cheers!