How exactly do ageing and pregnancy work in these movies? Judging by Selene and the other vampire characters, once bitten a vampire does not age but in the prequel Sonja is first seen as a child about Lucien's age. Did Victor just wait until she grew up before turning her? Can all female vampires get pregnant or was Sonja just special somehow? And was Selene ever actually physically pregnant with Eve/Subject 2 or was Eve a testube baby?
When is it ever said that these vampires can't get pregnant? Not sure if it's said how Sonja came to be, but she makes no mention of a mother. So we could assume that Victor groomed her to be one day a vampire, possibly while raising her as his daughter. As for the pregnancy, maybe the fact that it was a werewolf's seed had something to do with it. Or vampires can get pregnant in this universe.
I think its like they don't stop ageing per-se more along the lines of it slows down dramatically, Viktor does say her mother gave her life to birth Sonja, either that or vampires age to a certain point then it slows down, but i think that's how it goes.
While no longer Canon, the prequel novel Blood Enemy established that vampires could have children together, and "pure bred" vampires were a higher caste than those that were turned. Kraven managed to become an exception by pretending to kill Lucien. Much of the book contradicts later canon, however. Lucian wasn't the first transforming Lycan, and all three elders were stated to be pure bred vampires.
Vampires in Underworld are technically still alive (they are shown on several occasions to have heartbeats), therefore, there's no reason why they cannot procreate (in the sense that the bodily functions required for conception still appear to work). 'Pureblood' vampires like Sonja and David must stop aging at some point; Sonja was apparently supposed to be close to 200 years old in Rise of the Lycans, but obviously didn't look it. In the novelisation of Rise of the Lycans, it's mentioned that vampire births are quite rare. Therefore, it's possible for vampires to get pregnant/impregnate, it's just not very common. It's implied in Awakening and explicitly stated in Blood Wars that Selene and Michael conceived Eve naturally; Selene was in the early stages of pregnancy when she was captured and so didn't know she was pregnant yet. Presumably, Selene carried the pregnancy like normal, but whilst being kept in stasis by Antigen. It's also explicitly stated that David's parents were both vampires when he was conceived and that he was born a vampire, like Sonja. Werewolves and by extension Lycans seem perfectly capable of breeding with each other (though it's never made clear how Lucian came to be born; a popular theory is that his mother was already pregnant when she was turned into a Werewolf). As shown with Lucian and Sonja, and Selene and Michael, Lycans and vampires can conceive together, but it's probably even less common because of the whole 'vampire superiority' and 'Hybrids are abominations' debacle.
The nature of blood-bourne disease that creates "immortals" is somewhat contradictory:
Selene is exposed to Michael's lycanthropy-infested body fluids, but does not become a hybrid herself, yet when she drinks the blood of Alexander Corvinus, she becomes immune to sunlight.
While she was splattered with the bodily fluids of slain Lycans, Selene never consumed their blood and she never had any open wounds exposed to spilt Lycan blood.
William Corvinus attacked and killed numerous vampires with his claws and teeth, consuming their body fluids, but never becomes a hybrid.
Willaim could have eventually turned into a hybrid, much like his brother, but it is possibly his starvation and captivity prevented the transformation from catalyzing inside of his body.
Markus Corvinus seems to gain the memories of any creature whose blood he drinks, in any amount and in any situation, yet no other character does so. Lucian bites Michael and implants his memories, but the only other case of "transmitting" memories was when Selene awakened Victor.
It's more than Markus. Selene explains that only elders have the ability to properly arrange their memories into a coherent history. It's what she was attempting to do when she awakened Viktor, with less than perfect results, and in general, it's implied to be the way the elders manage to maintain consistent rule, despite their two hundred year bouts of hibernation. Michael's fragmented memories from Lucian are more likely a side effect of being turned rather than anything to do with blood, as seems to be the case with vampires.
And as for the rest, we could probably mark it down to "the Corvinus bloodline is weird and not all of the rules apply" since Markus and William are the progenitors of vampires and werewolves, respectively, and Alexander, as their father, probably shares at least some of the traits.
The Cleansers William killed were humans, not vampires.
Actually William probably killed tonnes of Vampires during the time in which he was free.
So... the only inconsistency here is Selene gaining a power boost and sunlight immunity by biting Alexander? Still weird.
And on a separate note, from the beginning, it was stated that Vampires and Lycans are both biologically compatible, and capable of breeding. In six centuries or more, why didn't Lucien just capture a female vampire, and get her pregnant? Or, just in more recent times, use artificial insemination? Hell, if he was squicked over the idea of rape, he could have used vampire blood on a volunteer. Instant surrogate mother.
In a non-canonical novel, it's claimed that the reason Sonya became pregnant with Lucians child is because they're both purebloods (i.e. born immortal).
Sonja never came into full-terms with the child so we don't know if it would have survived.
And since Sonja is The Lost Lenore, maybe Lucien wanted to avoid disrespecting her memory. She was the only woman he was ever with, and he doesn't want to tarnish that.
Marcus apparently gets a chance to kill all of the children he doesn't want every two centuries, with the only people close to strong enough to fight him lying in torpor. And, by vampire tradition, also completely dependent on him for reawakening.
It's not so simple. He may be strong, but he's not indestructible. The Death Dealers were all loyal to Viktor. They managed to subdue William in his beast form. They would have had an easier time with Marcus, especially in later centuries with more advanced weapons. Also, Marcus didn't want to jeopardize his chances of finding his brother.
By rights, the 'blood borne disease' thing that makes vampire/werewolf hybrids impossible should be lethal to both biter and bitten.
Viktor's internal Masquerade is dependent on very powerful Markus not getting cranky during his 100 year rule segments. While Viktor has taken care of the key to William's prison fairly well, that does not go for Markus deciding to shatter everything else.
When Markus finally does go ballistic, his father Alexander barely raises an eyebrow.
He was likely biding his time. Viktor was the only one that had any knowledge of the key or the location of the dungeon. Remember, Lucian's escape occurs during Viktor's reign, which wiped out a significant part of the vampire population - or at least those related to the high council. Markus would have awakened two hundred years later to find himself dealing with an entirely different coven loyal to Viktor and Amelia. It wasn't until Markus became a hybrid that he was was physically powerful enough to take out the entire coven himself. Regardless of the events of the first movie, things were bound to come to a head soon. With modern technology and biological science at his disposal, Viktor would have eventually come to realize that Markus's insinuation of supernatural heritage was a deception that no longer had to be entertained.
I wonder which race was first but I have a good theory, William and Marcus are super duper close, almost literally doing everything together, inseperable, best friends as well as twins, so one day while hunting, Marcus gets bit by a rabid bat (i assume the virus' were mutant forms of rabies, hence the bloodlust, they were already immortal) over the course of a few day Marcus becomes a vampire, get the powers, so william for the first time isn't equal to marcus, spurred by jealousy, he goes and looks for rabid creature to bite him, wanting something stronger than a bat, he ends up bitten by a wolf, the problem is the dose of rabies he gets from a wolf is much much more potent, unlike the bat which was enough to cause minimal diffirence, hence william becoming unable to turn back, also the reason Lucien was the first lycan is because his mother was bitten while pregnant with him, he basically became something along the lines of Blade. enough of the virrus to be one of them, but not enough to be unable to turn back.
According to official canon, Werewolves were first. William was bitten by a rabid wolf protecting his brother while they were on a hunt together, and it caused him to become a Werewolf. Marcus was later bitten by a bat, becoming a Vampire, though it's not really specified if this was intentional or not. As for the theory on Lucian's mother being bitten whilst pregnant, although it's not confirmed, it's one of the most popular theories out there as to how he became a Lycan.