The character order in a sense makes sense in that it's order of initial strength; first you start out with Simon who approaches the castle with naught but a leather whip and a burning desire for vengence, then we have Alucard who is a young vampire who lost a chunk of his original strength as Trevor due to his death/rebirth. Finally we have the well-trained and prepared Trevor.
Two bits at the price of one from Mirror of Fate: The game's acts are in Anachronic Order, with Simon first, then Alucard and finally Trevor as playable characters, but the three share the EXP accumulated. This at first glance causes some Fridge Logic and allegations of Gameplay and Story Segregation, as by the end Trevor is far more experienced than his future self Alucard. Nothing of the sort, it is actually perfectly explainable: Vampire Trevor has awakened from 30 years of slumber, so he is far from being in perfect shape, both physically and emotionally, with new unsettling powers to get used to; at the end of his act, he has recovered a mere fraction of his old strength. Still, there seems to be one last discrete discrepancy: Trevor, at his prime, could not defeat Dracula, yet the far weaker Alucard succeeded. This is actually easier to explain: Alucard does not defeat Dracula alone; he is the player character alright, but he's fighting in tandem with Simon, and the combined experience of the two by that point easily surpasses the lone Trevor's.
Why does Gabriel rename Trevor Alucard when he turns him into a vampire? He probably didn't know his name, Trevor never told him and the Mirror Of Fate doesn't seem to be capable of creating sound.
