The plot of A Family Reborn is the Fire Nation Royal Family: Zuko, Azula, Ozai and Ursa are reunited and that starts a trip into the minds of Zuko, Azula, Ozai and Ursa now that they are reunited. It will feature character breakdowns from the whole journey of seeing their mother again and will also feature as the main plot on Azula's characteristics from seeing her mother again.
In Book-2 four years have passed since Azula was captured and Republic City began construction. Republic City is now built and so is Air Temple Island. Book-2 will feature, Team Avatar, challenged with ruling the United Nation- all the different bending groups now combined living in the same area- will lead to neighbourhood, "social class" issues and normal government problems- crime,work etc.
It will also feature Azula's journey to regain her bending. She will embark on a rip to a place only Avatar's have been too, in search of what was lost. Secrets will be revealed... remember:
"There are secrets you want to keep in and secrets you dare not let out, but if two can keep a secret, that means one of them is dead"
— A Family Reborn