A brother whose mom has schizophrenia asks if he should go to the mosque. His mom prevent him from going because she believes there are enemies who may harm him and she is scared. Should he obey her or go to the masjid since she is mentally ill ?

You should ask the doctor this: 1. Is it going to make her worse? 2. Can she be left alone? 3. When she says something like this, can you actually calm her and leave, or is it going to get worse for her, and someone has to, for example, stay by her side and reassure her? I'd see what the doctor says.