Assuming what OP said is true, he didnt have substantial autonomy so cant be ethically held responsible for killing his half brother. Or do you believe people with compulsions/hallucinations are in complete control of their actions/autonomous?

The landlord/police arent necessarily at fault unless they understood the situation in which case, they definetely could have handled it better. The boss was maliciously compliant with only doing the bare minimum. Knowing his employee had these circumstances and that there was a simple solution but yet doing nothing is neglectful for vulnerable people in society.

It would probably be more obvious to you if he had a physical handicap and was being neglected accomodations and thus causing the events leading to the suicide.