Board Thread:Anime/@comment-36552187-20180913104607/@comment-1327106-20181002021752

For answers:

1) I believe Kenny must have told Levi. I think he says "he said" when referring to Kenny during his conversation with Mikasa, which means even if it seems odd, Kenny actually shared that information with Levi.

2) Levi likely did not consider he might be related to Mikasa for the same reason we never considered it before now. It's incredibly unlikely that a random person you meet is related to you.  Sometimes it happens and they're your distant cousin!  But usually they're not.  Unless there's reason to think they could be (like the same family name), it's a safe be to assume that they're just another unrelated person.

The best athletes in the world aren't all related to each other. It's perfectly normal for unrelated people to reach a similar athletic peak, and if you watch any sports at all you've probably seen some godly performances that are far above what the average human can do. Sure, sometimes they're siblings, or parent/child with decades between performances, but most of the time they're done by unrelated athletes even if they're in the same sport.

Levi doesn't know anything about bloodlines or this Ackermann stuff prior to this particular story arc, so he has no reason to think that Mikasa is related to him.