
The first is City Infernal. It follows Cassie Heydon, a goth chick whose twin sister, Lissa, commits suicide after catching Cassie making out with Lissa's boyfriend, a goth club bartender named Radu who is described as looking like Nosferatu with muscles.
Some times later, after therapy and failed suicide attempts, Cassie's father moves him and his daughter out to the country, but Cassie discovers that the house belonged to a Satanist who raped women and then sacrificed the babies to Satan.
To make things weirder, Cassie finds three ex-residents of Hell living in her house... and only SHE can see. It turns out that she's an "Etheress", a legendary myth in Hell. Being born a twin on an Occult Holiday, who and whose twin was suicidal but only one succeeded in suicide and were both virgins, the Etheress has vast powers in Hell. She crosses to Hell and discovers that it is in fact a vast city that is a polar opposite of ours.
She later comes across a plot to bring the horrors of Hell to Earth... and the Etheress is the key!

The next is Infernal Angel.
Continuing some time after City Infernal, Cassie has found herself in an insane asylum, where she is told by a Caliginaut angel that she must return to Hell.
Meanwhile, Lucifer has begun work on a means to allow a part of Hell to occupy an exact portion of Earth as a means of a demonic plan that stretches across space AND TIME!
And if that wasn't enough, a male counterpart to the Etheress, the Etherean, has found himself in Hell, but what are his motives?

The next, and (currently) last, is House Infernal.
This time, the main character is Venetia Barlow, a young woman working to fix up an old priory house that was in fact built by a Satanist, who has created the house under demonic influence. And the priory house is at the heart of a criminal investigation involving blood-harvesting Satanists, a plot by the demonic Antipope Boniface, and an effort by two humans, a priest and a recent member of the Human damned, to stop a plan by Boniface to bring a brood of unholy monstrosities into our world.
I highly recommend it to fans of dark fantasy or for fans of Clive Barker.
There's supposedly a movie adaptation in talks.
Personally, I wish they'd make a video game based on it. It'd be a mix of Devil May Cry, GTA, Diablo, Alice: Madness Returns and various other elements. Basically, an open-world action-RPG with adventure, beat 'em up, and hack 'n' slash elements.
As for the web series City Infernal: Redemption is Hell, IDK what that is, but doubt it's related to this awesome book series.