We don't know much about the Shepherdson family other than the fact that they are the rival clan of Huck's adoptive family, the Grangerfords. The Shepherdson plantation is about five miles away from the Grangerford pad, but evidently, that's still too close for comfort. The two families share the same steamboat landing as well as the same church—the one place where they can peacefully co-exist, albeit with their guns locked and loaded resting between their knees.
Despite all the hatred, the Grangerfords genuinely respect the Shepherdsons. "There ain't a coward amongs them Shepherdsons" (17), Huck says. But when Harney Shepherdson, one of the clan's studly sons, runs away with Sophia Grangerford one night, that mutual respect doesn't stop the families' violent hatred from claiming many lives on both sides. (You may also want to check out what we have to say about The Grangerfords.)