What did you end up doing? I am in the similar situation.
It requires
1. Proof of PR/Citizenship of sibling
2. Proof of Residency in Canada of Sibling
3. Proof of sibling relationship
4. Family Member Proof of Status
I think I should put PR card in 1. Bank statement in 2. Passports and birth certificate in 3. Still confused on 4. ( I should attach all the 3 and submit I guess)