Board Thread:Episode Discussions/@comment-3261234-20150416133517/@comment-3279282-20150416172701

No idea who Sho and Judai are, but as I said, it's usually used for superiors, older brothers are normally called (o)niisan. The difference is that oniisan is familiar, aniki is not.

And no, it wouldn't be speculative, because it would be the common thought everyone who watches the episode would have. As I said, we likely won't be getting more information about their status and not to say they're siblings despite them calling each other sisters would be even more speculative. We have one argument (the honorific) pro and zero arguments contra this case.