The myth of vampire fear of sunlight, garlic and cross stemmed from two things: Vampire Lords, whose massive use of dark magic forbade contact with sunlight, and these Night Brothers. They act as a foil to their more brute-force inclined comrades the Havenguards. They act as assassins, spies and informants in a vampire army, a post that required much less number and far more eliteness from their membership. This is why they were usually drawn from the upper-medium class, those who had much more stake in the running business of the vampire society than the average citizen.
All of the Night Brothers, as the name suggested, are members of the Temple of Blood, a secretive cult with infamous reputations even among vampires. Their dealings included sacrifices, blood rituals and inseparable brotherhood with one another. The fact that the Temple of Blood was feared by the lesser vampire citizens speaks volumes about their infamy.
While most of their works are done in the night, as their name suggests, when the time comes, they would march into battle together with their brothers. In a pitched battle, their role is strictly reserved to flanking, and their equipment reflects that - light coats, no shield and a two-handed falx-scythe, with copious amount of black-red facepaint. Their reputation preceded them, and their frightening presence could scare off all but the most fearless of foes. In a vampire army, their elans and esprit de corps is second to none because of their religious bonding with one another. However, their lack of armor meant they would be torn apart by many opponent who could ward off their initial impact. Most opponents, though, would not manage that.
Historically, their church was founded in late 4th century AD as a foil to the growing Catholic church. Needless to say, their moral ambiguity and the general intolerance of Christianity to "heresy" in that age meant that their religion was one of the first to be actively forbidden and purged by the Catholic Church. This, and the fact that they were no less bigoted than the Catholics themselves meant that they were the most vehement Vampire Hunter-Hunters. An uncredited source stated that roughly ninety percent of all vampire hunter casualties in covert operations over the past millenium were owing to the ferocious Night Brothers and their fearsome falxes.