It makes sense if you imagine this all happening in the writer's head.
"the (title) 'Sisters' jumped in front of the (surname) 'Blythe'" - so we have "the Sisters Blythe"
"somewhat like the Brothers Grimm" - we naturally think it this way, for these particular storytellers. We don't think "the Grimm brothers", even though that's the typical word-order for such a description.
"and there was little I could do to stop it" (from happening). - the writer could not stop automatically thinking of them as "the Sisters Blythe".