Nephilim's Savior Series is about Alec and Gabby. There are two books out and one Novelette—Tatia and Viktor's story about how they got together as mates. The Novelette is set before the Nephilim's Savior story, so it could be read as a standalone. However, it might be confusing to some when references to Nephilims or Fallen Angels are mentioned.
Vis Novella will focus on Daemon and Celeste's story and will pick up from Vis book 2.