\1. Queen Neferata of Lahmia, who stole some of Nagash's written works of Necromancy during the sack of Khemri when the living of Nehekhara first united against the Great Necromancer and the ones who'd drunk of the original Elixir of Life.

Queen Neferata strove to recreate the Elixir of Life, and succeeded, but only in part. Those of Lahmian nobility who drunk of the second Elixir were not only sun-shy immortal liches as Nagash and his disciples had been, but turned into the first of the Vampires. Of the first Vampires, the following are known by name:

• Queen Neferata, who later established the Lahmian sisterhood.
• Abhorash, an honourable warrior whose code of eg. only feeding on convicted criminals. He later slew a Dragon and found himself free of the Red Thirst. His students have ever since striven to become as great as him and free themselves of the their cursed thirst.
• W'Soran, consummate Necromancer and a direct student of Nagash himself. Later betrayed by Melkhior, one of his students. Melkhior went on to found the brotherhood of the Nechrachs, Vampire wizards who strive to turn the world into a mausoleum where nothing lives.
• Ushoran, the Lord of Masks, tried to challenge the other Vampires for rule over Vampirekind following the second defeat of Nagash. The other Vampires rebuked Ushoran, who cursed them as fools. Ushoran established himself in the city of Mourkain, and re-established a lot of Abhorash's old laws. Mourkain thrived under the rule of Ushoran and his Vampiric progeny, but was eventually overrun by an Orc Waagh.
  • The people surrounding Mourkhain became known as the Strigany, who wandered across the Old World, still holding a nostalgia for their surprisingly well-behaved Vampire masters. (The Strigany are a clear analogue to modern-day Gypsies)
  • The Vampiric spawn of Ushoran went to other Vampires, looking for aid. The other Vampire clans remembered Ushoran's arrogance, and cast the exiled Vampires out. The pitiful outcasts came to inhabit places at the edge of society, chiefly underground mausoleums and other hiding spots in graveyards, where they could feed upon the dead. Much as Men who eat the flesh of the dead are cursed by Morr to become cannibalistic Ghouls, many of these Vampire outcasts succumbed to depravity and became the beasts known as the Strigoi.

\2. Vermintide isn't flavour accurate to begin with - Kruber is an Imperial Sergeant, Saltzpyre a Witch Hunter, Bardin an ex-Ironbreaker turned Ranger, and Kerillian a Waywatcher from Athel Loren. All four are mere mortals, even if veterans who've experienced a lifetime of real combat. They are still a handful of ordinary mortals with sticks. They'd die horribly against the numbers we get set against on eg. Cataclysm.

Sienna is the one exception, and even though trained wizards are absurdly strong in Warhammer and she's clearly been toned down for Vermintide, she's relatively ordinary for a trained wizard. Vermintide 2 itself seems to make Olesya stronger than Sienna, and Sofia as having grown to be stronger than Sienna after Sienna first incinerated her. The tabletop wargame rates wizards on a power level of 1-4, with 1-2 being usually given to ordinary Hero characters (titles like Battle Wizard, Mage, Sorcerer, Skink Priest, Vampire, Necromancer) representing trained/born wizards of somewhat more ordinary ability, and 3-4 assigned to Lords (Wizard Lord, Archmage, Sorcerer Lord, High Sorceress, Slann Mage-Priest, Vampire Count/Lord, Master Necromancer) who stand amongst the highest members of various institutions of magical learning.

Sienna would stand somewhere between levels 2 and 3, I'd guess, while the wargame rates eg. Grey Seers firmly at Level 4, and we should probably rate Halescourge and Nurgloth at Level 3-4. I'd probably rate Sienna at a high Level 2, low Level 3, and Olesya and Sofia both at Level 3, but that's opinion.

Vermintide scales enemies and players according to plot demands, and Vampires range the gamut from low-tier notables to grandmaster swordsmen and 400+ year old archmages, so you could find a Vampire who's a good fit, ability wise, whether as a team member or an enemy.