Applications for mentally disabled brother

[Noda Mark]

As a Canadian citizen, I intend to apply for my Sudanese brother who is currently outside Canada through the program link provided. I will act as the anchor in the application process. My brother, aged 39, has a mental disability, Can he be the primary applicant, as my parents are not eligible for this program?
If so, I seek guidance on whether I can apply on behalf of my brother, and I also need clarification on who is authorized to sign documents such as Schedule A and other related forms.