I feel this person needs to involve their local authorities/agencies, and I know they may consider that shameful or wrong or dangerous, but they need protection and backup. I do believe that social services will help, if they allow it. Raising the rent a little, trying small or incremental change to the situation---I think that won't work and the abuser may escalate. Evicting them is going to take real enforcement.

I wish the advice was better. I am worried about this person.