My advice is to be honest with IRCC. Any lie or mis-information (not disclosing something that was asked about in the forms) can be seen as misrepresentation. IRCC is usually forgiving if applicants come clean before it's discovered by IRCC.
By the time if IRCC discovers it and request for PFL, that may be too late. Is your siblings on work/study permit? Waiting for PR application? There is no real reason to hide the relationship since I don't see any benefit on hiding. (If both of you are in Canada, then there is no issue with each other's background or criminal check which may be the only reason to hide it... )