Are step children related?

Mr X and Ms Y are common law partners. Each of them has a son from a previous relationship. Are the sons related for the purposes of the Income Tax Act (Canada)? The CRA says “yes” because the step brothers are deemed to be the children of common parents under paragraph 252(1)(c). See Neal Armstrong summary of CRA technical interpretation 2015-0584261E5 dated November 3, 2015.