But we don’t even know if there is a third brother! ^_^ We have only Mycroft referring to ‘the other one.’ He could be talking about anybody. He could be talking about Moriarty. Or Lupin III.
Oh man. If there’s a third Holmes brother, I hope he’s Lupin III. Or Raffles. That’d be amazing. Or, maybe it’s a Holmes sister.
(Did you guys hear the Darth Vader voice? Because I totally just said that in the Darth Vader voice.)
But yeah, I have no idea whether there is a third brother, if his name is Sherrinford, or whether Mycroft did something to him (I assume not, since he’s still on cordial terms with his parents and, given their apparent love for their children, I think that their relationship would be strained if something like that had happened).
But I’m not too concerned. Even if they do show up, they’re hardly going to be lurking around in every episode (unless they turn out to be the plot hook for the season, of course).