I'd go for Alucard being more of the serious older brother role, with Dracula as the father, Lisa/Elizabeta as the kind mother, Leon as the patriarch of the Belmonts, and former best friend of Drac, whose best friend is now Death (or Death could fill the uncle role?). Shaft would be someone in the employ of Dracula, who's an annoying, slimey sort (and filling a Smithers to Mr Burns role). Hector and Isaac could be apprentices of Dracula's, with Isaac perving a lot on Alucard most likely, to his annoyance. Yoko is Mina's best female friend, and a co-worker of Alucard's, along with Julius Belmont. Drac doesn't approve of Alucard and Soma's friendships with the Belmonts.