Why Was Credence On That Ship?
If Grindelwald was being truthful and Credence is in fact the fourth, and previously unheard of, Dumbledore sibling, then why he was on that ship (the Titanic?) along with Leta and Corvus Lestrange Jr.? Escape, concealment and opportunity all seem like possible reasons. According to the script, Credence was with his “Aunt,” but that is far from definitive. An aunt could be: an actual relative; a liar; someone using Polyjuice Potion, or; someone controlled under the Imperius Curse.