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If Ocarina of Time's Link were a descendant of Skyward Sword's Link and Zelda, he would be part of the Royal Family... And he isn't. The only characters proved to be descendants of their own incarnations in other games are Zelda and the King, as they are always part of the Royal Family of Hyrule.

they could be like really not so related long lost cousins

^^ I never thought it that way... Thanks, man! So Link married his long lost cousin. Some crazy things are happening at Hyrule!