New duplex purchase with current tenants!

[Manju Nat]

Hello fam,

I closed on a duplex last month in Greater Seattle area. There are currently tenants in both the units (month to month) who have lived there pretty much for the last 20 years and are elderly. Both units are subsidized by the housing authority that pays 80% of the rent and they are below market rents (negative cashflow currently). I would like to ask one of the tenants to vacate so that I can make interior updates and rent it for market rent. Housing authority said I need to give an usual 20 day notice to vacate but are there any other laws (pandemic related or otherwise) I need to keep in mind? Also, has anyone been in a situation where you had to ask elderly tenants to vacate? I obviously want to make cashflow but want to deal with the tenants in a humane way. Any inputs? 

Thanks!