Julia, who is Isaac's sister, is a witch who escaped the witch hunts and inexplicably looks identical to Hector's wife Rosaly, who was killed in said witch hunts thanks to Isaac. Could it be that Isaac framed Rosaly both to piss off Hector and to protect his sister...?
In every Castlevania game, Dracula's Castle is always filled with numerous monsters for you to fight. This game seems to justify this by introducing the Devil Forgemasters — people who are allied with Dracula, possessing the ability to summon monsters. Among the various Innocent Devil evolutions that Hector can choose, there exists Gargoyles and Golems, which are some of the most common mooks throughout the franchise.
The Skull Bomb that the Proboscis Fairy uses isn't a very useful weapon as it does minimal damage to enemies and can even damage Hector. But against a certain penultimate boss it takes out a whopping 25% of his HP. Why is this? Perhaps the skull on the bomb, which is commonly associated with Death, might have something to do with it.
There is actually some Fridge Brilliance when one considers a subtle piece of foreshadowing of Zead really being Death. Aside from obvious points like him summoning the scythe blade from his sleeve and antagonizing Saint Germain and mentioning "nobody escapes from me", consider where Germain later gets trapped at thanks to Zead: the Clock Tower. The place where in more of the modern Castlevania titles of the time Curse of Darkness was released, Death was commonly fought at or guarded due to how close it was to Dracula's quarters!
The concept of Devil Forgemasters only exists in this game, but doesn't exist in other Castlevania titles. Why do we not see them? Well, there's a couple of reasons why.
The first is that while they can bolster Dracula's forces, the Innocent Devils they summon and create are ultimately loyal to their creator, as Dracula gets a first hand demonstration of against Hector. If they cannot be loyal to him, then he has no need of them.
The second is that given Hector's prowess in battle against Dracula and his betrayal beforehand, Devil Forgemasters can ultimately turn out to be more of a danger to work with than to kill.
As said above, Death originally thought that only a Devil Forgemaster would do to resurrect Dracula. However, when he later found that summoning Dracula simply needs blood sacrifice of pretty much anyone, there's no more need to even keep a Forgemaster present, much less work with one.
Finally, Dracula's Curse, which plagued Europe and spurred humanity into self-destructive actions through anger and hatred, was cast aside by Hector who gloated about it to his face before he died. Dracula would naturally be salty about that and as a result, his thoughts on working with devil forgemasters would be sealed to "never hire".