Not possible when Milah met Hook for the first time when Baelfire was already like 7 years old, as shown in “Devil’s Due”. Rumple and MIlah’s marriage also didn’t get rocky until Rumple injured himself to get out of the war, when Baelfire had already been born. Not to mention, blood magic has been used between Rumple and Baelfire to further prove that they are father and son.