Washington tenant laws

[Amber Bellin]

So I am asking this question for a friend who lives in another state and I am unsure of her rights. She owns her home and in order to make ends meet she let a "friend of a friend" move into her basement about 4 months ago. They have no written contract and he pays her in cash (never on time) $300/month. Well 5 days ago he mentioned to her that his cousin who lives in Kentucky was in a "bad situation" and needed to move up here. He left the next day to go see her. She learned today that he has packed her and her things into his car and is planning on moving her in! This was never discussed in anyway with my friend who is trying to get her house ready to sell. They never asked permission to move on another person let alone rent $. This man, of course, claims that she told him it was fine and his cousin could stay "as long as she needs" It's a lie but no one can prove either side. This man is staring to get belligerent over text and I am now concerned for my friends safety as well as the state of her home... I would like to do this diplomatically but I don't even know what legal options she has here. Advise? Tips? Suggestions?