Visitor visa, help with form 5645e

Hi, my parents are applying for visitor via for Canada. While filing the form imm 5645e, he has filled his and mum's details and thier children's details. in section C it asks for brothers and sister details.

My question is does he only need to fill his borthers and sisters detail, or my mum needs to fill as well but in a seprate form to enter her siblings details ?

Thanks