I don't know for sure as the 'pll kids story' is not well - defined here. But it could have characters like kids of different ages, perhaps a brave little boy, a kind - hearted girl, and their friends.
There's no way to tell just from the title who the author is. It could be a relatively unknown fan who just wanted to share their take on Spencer's story with a love theme. It might be someone who has been a long - time PLL fan and was inspired to write this fanfic based on their love for the character Spencer.
A possible kidnapper could be a new character introduced in the fanfiction who has a dark obsession with Emily. This person might have been watching her from afar, learning her routines, and waiting for the perfect opportunity to kidnap her. They could be motivated by a desire to have Emily all to themselves, or perhaps they believe that Emily has some special power or knowledge that they want to extract from her.
Another potential antagonist could be a new character. Maybe someone who has a vendetta against Aria's friends and is using Aria as a way to get to them. This new character notices that Aria is tired and weak, so they target her specifically, causing more chaos and confusion in the PLL fanfic world.
A new character could be the main villain. Maybe a person who has been obsessed with the Liars' story and wants to recreate the drama and chaos for their own twisted reasons.
Well, without more context regarding 'PLL Book 12', it's really difficult to name the 5 novels. It might be that this is a very specific collection within a certain series. Maybe if we knew more about the overall theme of the PLL series, we could make a better guess.
I'm not sure specifically which 'pll' you are referring to. It could be 'Pretty Little Liars'. If so, it's a story full of mystery, secrets, and drama among a group of friends who are being tormented by an anonymous 'A' who knows all their secrets and uses them to play cruel games. There are lots of plot twists and turns as the girls try to figure out who 'A' is while dealing with their own personal issues like relationships and family problems.
Charlie could potentially be a character from another show or story that the author of the fanfic is incorporating into the PLL universe. This character might have abilities or knowledge that put Emily at a great disadvantage. For instance, if Charlie has some sort of supernatural power or access to secret information, it could be used to corner Emily and make her feel like it's 'game over' in the fanfic.
Since it's an Eriza PLL fanfic, Eriza is most likely one of the main characters. There may also be other characters from 'Pretty Little Liars' that interact with Eriza in the context of this love story. But without reading it, it's hard to say exactly who else.