I was under the impression, canon or not, that the reason the Graves and Morris clans got the VK Whip was due to there being no male heir around/ready at a given time; therefore, the son of the most-related clan would get the honor. But really, there could/should be a story where a female Belmont has the honor of the VK Whip (IE: a retcon Sonja) and then starts her own line with a new name that later has to use the whip.
But, anyway, I thought that Castlevania has been trying to move beyond the whip with all the magic and sword use up front lately. Sad, because the whip has so much unused gameplay potential and is one of the things that makes Castlevania unique.