They are currently offering 14% up to 20% on a particular project they are working on. 

But, that requires analysis.Also, there are many other investment opportunities with returns above what most real estate is offering now.And, I think the assumption is that there are loans on ALL the properties?

Still haven't made up my mind but here is what I can offer. 

Can we even legally get him out?

Therefore, even if an applicant acknowledges her credit history and offers a larger deposit, landlords must adhere to the legal limits set by the state.

We have had offers of $430K on it few months ago as was.

ANYONE can put in an offer.

Since ADU rules were liberalized by Seattle in 2019 (one attached + one detached allowed on any single-family lot, no owner-occupancy requirement, no restriction against separate sale). a number of spec builders in Seattle have been building what may look like a townhouse triplex but is legally a single family primary homes plus two ADUs, one attached and one detached. 

Tools like LegalNature offer templates and document storage for compliance purposes.

You contract with the seller should spell out exactly what the risk are for him; further, you should not do this deal unless (1) the seller utilizes the services of an attorney to advise him (2) you have the cash or credit capacity to payoff or refinance the loan if it is accelerated due to the due on sale clause and (3) proper safeguards by way of third party servicer, escrow, legal documentation, are adhered to.It seems you may have a big winner; however, it’s just these that lead to lawsuits if not handled properly.