While Mirror of Fate's main story thread involves Trevor Belmont (the son of Gabriel, from the first Lords of Shadow) looking to avenge the death of this mother—who was in fact slain by Gabriel after his eventual transformation into Dracula—the game ropes in three other members from the Belmont lineage and the series' history, including Simon Belmont and Alucard.

That's particularly odd. So, Marie isn't Trevor's mother? That makes Trevor and the entire Belmont clan part-vampire. In the original canon, the same thing happened with the hinted tryst between Alucard and Sonia Belmont in Castlevania Legends which kind of screwed up the entire series before Igarashi gave it the boot.

This kind of cheapens the original Lords of Shadow since Gabriel's entire quest revolved around on finding the God Mask to resurrect Marie. So, Gabriel honors Marie's memory by banging some other chick then murdering that chick. What the? It would make more sense to me if Trevor was Gabriel and Marie's son, even if he was never mentioned in the original Lords of Shadow. Then, Tevor could be looking for his mother's murderer who is, in fact, also Gabriel. Cue I-am-your-father moment and at least the Belmont clan is still human.

At the same time, I suppose you have to explain Alucard if he's still Dracula's son in the new canon (he better be) which means Gabriel is going to have to have a child with a human woman after becoming a vampire which still kind of cheapens the original Lords of Shadow. I suppose it depends on how MercurySteam handles it. Hmm...

If I were writing the story I would have had Gabriel father a a child with that vampire chick, Laura, and have the result being Dracula. This way the Belmont's mission to eradicate Dracula is more or less a way to destroy what their ancestor helped create.

No offense, but I'm glad you're not writing the story then. Laura has the appearance of an 11 year old girl. What you're suggesting would be an abomination. Also, she's dead. She forces Gabriel to drink all of her blood so that he has the power to defeat The Forgotten One. He becomes Dracula by absorbing The Forgotten One's power.