Question: how could credence be related to dumbledore?
Answer: So at best Credence could be Albus's half-brother, if against all odds he was conceived in Azkaban by Dumbledore's dying father. Grindelwald encourages Credence/Aurelius to kill his brother Albus before he does. ... The films imply that Ariana Dumbledore, like Credence, was an Obscurial.