Dinesha in sacramento, ca

My mom has been living in Vallejo her entire life and has never experienced anything of this nature. For the last 9 years she’s been residing in a small apartment complex on Sacramento St. Within these 9 years she has lived in 2 separate units. She moved in Jan 2005 and was relocated from the 1st unit July 07 due to Mold issues. Since July 07 until present she has been living in the 2nd unit. My oldest brother came to live with her Feb 2014 and now has been hospitalized for the past two weeks. One week before he was admitted into the hospital he began vomiting consistently and running a high fever. After he was admitted into the hospital he has had two surgeries. The first one was to remove a swollen cist in his neck and determine what was making him sick. After all the test where complete the doctors reported that he has fungus inside is body due to black mold growing in my mom’s apartment. He has been told that his immune system may never be the same again. Who is to be held responsible for this? What are my legal right? Please help.