(And, please, for everyone's sake, don't make either Mycroft or Sherlock an earl or a duke. Just...don't. It screams "this story was written by someone who didn't know what she was doing" in letters fifteen feet high.)

And please bear in mind that Sherlock is Mycroft's younger brother so that there's double fail if Mycroft's an earl and Sherlock's a Duke or Mycroft has no title and Sherlock does.

But I agree in general on the "avoid titles" bit.