Name: Jane Yellowrock series
Author: Faith Hunter
Length: There are 15 novels in the series and many short stories. Of the requested characters, Leo and Jane show up in the first book, Skinwalkers, which is 320 pages long. Grégoire is a regular character starting in the third book, Mercy Blade.
Sub-genre: Urban fantasy, vampire
Why it's awesome: Really chewy urban fantasy that gets more complex throughout the series without ever becoming a confusing mess. Protagonist is a Cherokee shapeshifter and vampire hunter who gradually gets drawn deeper and deeper into the vampire politics of New Orleans without ever losing her individuality. Great worldbuilding. Lots of different kinds of supernatural characters and magical/supernatural powers. Multiple factions and alliances and rivalries. Most of the characters are shades of gray, but a few are out-and-out evil because characters we can really hate are fun, right?
Any other important information to know about: All the novels are available in print, audiobook, and ebook editions.