Sad but true. You can always appeal and hire an immigration lawyer but the chances are slim, almost nil. During the application of PR, naka-state naman sa mga forms na pag hindi idineclare ang family members eh hindi na nila mai-sponsor in the future. Very clear so you cannot argue na hindi alam.
Pwedeng palabasin na aampunin yung bata kung hindi sila listed as fathers sa birth certificate, which I doubt. Basta mahirap lokohin ang Canadian government. Scary. They have ways to verify the truth. The visa officers are also trained to detect fraud. Sa konting inconsistency sa statement, makikita nila. Baka ma-compromise ang PR status ng mga kapatid mo kung hindi magiging solid proof ang arguments.