I dunno, the whole "main hero is actually related to the villain" plot has been done so many times already, what's wrong with keeping it simple & having them be nothing more than longstanding rivals due to a falling out in the ancient past?
I like the idea of the Belmont family remaining the holiest in a world full of evil, not being tainted by vampire blood or anything else other than sheer will & Belmont Warlord Chromosomes.