The Romance Genre has a GENIUS marketing ploy out there in the book world to absolutely suck in the readers and keep them hooked - sibling/location series books. These are books series that I would almost label novella series, where the author creates a family or a town with either 4 to 5 siblings or close friends. Then the author intertwines all the stories, writes books that are on average 180 - 240 pages long, (note, the books I'm using as an example are actually longer books than normal for these types of series) and sells them for 99 cents to 4.99 each. After cleverly getting you invested in these characters, you can find yourself automatically purchasing the next book in the story because you have to know what happens to all these people. The book series below has a whopping 7 family members in this branch, and then also travels to the other side of the marriages for even more large families. Altogether you could end up buying over 25 books to discover what happens to all of these characters, all while keeping up with the ones you already know. While this may involve some heavy outlining for the the author - it is MARKETING GENIUS!
The English Family: Barrett, Fitz, Alex, Stratton, Weston, Kate, Tom & Eleanora
The Winslow Family: Brooks, Preston, Cameron, Christopher & Jessica
The Rousseau Family: Jean-Christian (J.C.), Etienne (Ten), Jacqueline (Jax) & Madeleine (Mad)
The Story Family: Alice, Margaret, Elizabeth, Priscilla & Jane
The Ambler Family: Bree, Dash, Cort & Sloane